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1. Shard Calculation

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Response:

Calculated Shard: 152 (from laksa153)

2. Crawled Status Check

Query:

curl -X POST \
  'http://laksa152.int.ahrefs:8124/' \
  -H 'Content-Type: text/plain' \
  -H 'X-ClickHouse-Database: crawler3' \
  -H 'Authorization: Basic YXBpOg==' \
  -d 'SELECT getAhrefsURLFromUnparsed(src_unparsed) AS found_url, ifNull(toUnixTimestamp(download_stamp), 0) AS crawl_time, ifNull(toUnixTimestamp(props_url_first_seen), 0) AS first_indexed_time, download_http_code AS http_code, src_unparsed AS src_unparsed, src_root_hash AS src_root_hash, history_drop_reason AS history_drop_reason, meta_title AS meta_title, meta_descriptions AS meta_descriptions, attrs_boilerpipe_text AS attrs_boilerpipe_text, attrs_markdown AS attrs_markdown, attrs_readable_markdown AS attrs_readable_markdown, meta_canonical AS meta_canonical FROM crawler3.page_info_local FINAL PREWHERE (src_root_hash, src_unparsed) IN ((getAhrefsRootHashFromUnparsed(getAhrefsUnparsedNoserviceFromURL(\'https://en.wikipedia.org/wiki/While_loop\')), getAhrefsUnparsedNoserviceFromURL(\'https://en.wikipedia.org/wiki/While_loop\'))) FORMAT JSONEachRow'

Response:

{"found_url":"https:\/\/en.wikipedia.org\/wiki\/While_loop","crawl_time":1774026635,"first_indexed_time":1376027366,"http_code":200,"src_unparsed":"org,wikipedia!en,\/wiki\/While_loop s443","src_root_hash":"17790707453426894952","history_drop_reason":null,"meta_title":"Loop (statement) - Wikipedia","meta_descriptions":[],"attrs_boilerpipe_text":"From Wikipedia, the free encyclopedia\nIn\ncomputer programming\n, a\nloop\nis a\ncontrol flow\nstatement\nthat allows code to be executed repeatedly, usually with minor alterations between repetitions. Loops can be used to perform a repeated action on all items in a\ncollection\n, or to implement a long lived program.\nLoops are a feature of\nhigh-level programming languages\n. In\nlow-level programming languages\nthe same functionality is achieved using\njumps\n. When a program is\ncompiled\nto\nmachine code\n, looping may be achieved using jumps; but some loops can be\noptimized\nto run without jumping.\n[\n1\n]\nUsually, loops are expected to run for a finite number of iteration.\n[\ncitation needed\n]\nWithout proper care, loops may accidentally be created that have no possibility of terminating. Such loops are called\ninfinite loops\n. The problem of determining whether a program contains an infinite loop is known as the\nhalting problem\n.\nA\nconditional loop\n(also known as an\nindeterminate loop\n[\n2\n]\n) is a loop that determines whether to terminate based on a logical condition.\n[\n3\n]\nThese loops are flexible, but there exact behavior can be difficult to reason about.\n[\n4\n]\n: 368 \nA conditional loop is usually composed of two parts: a\ncondition\nand a\nbody\n. The\ncondition\nis a logical statement depending on the state of the program and the\nbody\nis a block of code that runs as long as the\ncondition\nholds.\n[\n3\n]\nA common misconception is that the execution of the\nbody\nterminates as soon as the\ncondition\ndoes not hold anymore; but this is usually not the case.\n[\n4\n]\n: 368 \nIn most programming languages, the\ncondition\nis checked once for every execution of the\nbody\n. When the\ncondition\nis checked is not standardized and some programming languages contain multiple conditional looping structures with different rules about when the\ncondition\nis assessed.\n[\ncitation needed\n]\nA\npre-test loop\nis a conditional loop where the\ncondition\nis checked before the\nbody\nis executed. More precisely, the\ncondition\nis checked and if it holds the\nbody\nis execute. Afterwards, the\ncondition\nis checked again, and if it holds the\nbody\nis executed again. This process repeats until the\ncondition\ndoes not hold. Many programming languages call this loop a\nwhile loop\nand refer to it with the\nkeyword\nwhile\n. They are commonly formatted in manner similar to\nwhile\ncondition\ndo\nbody\nrepeat\nInstead of the keywords\ndo\nand\nrepeat\nothers methods are sometime use to indicate where the\nbody\nbegins and ends, such as\ncurly braces\n[\n5\n]\nor\nwhitespace\n.\n[\n6\n]\nFor example, the following code fragment first checks whether\nx\nis less than five, which it is, so the\nbody\nis entered. There,\nx\nis displayed and then incremented by one. After executing the statements in the\nbody\n, the\ncondition\nis checked again, and the loop is executed again. This process repeats until\nx\nhas the value five.\nx\n← 0\nwhile\nx\n< 5\ndo\ndisplay(\nx\n)\nx\n←\nx\n+ 1\nrepeat\nDo-While loop flow diagram\nA\npost-test loop\nis a conditional loop where the\ncondition\nis checked after the\nbody\nis executed. More precisely, the\nbody\nis executed and afterwards the\ncondition\nis checked. If it holds the\nbody\nis run again and then the\ncondition\nis checked. This is repeated until the\ncondition\ndoes not hold. This is sometimes called a\ndo-while loop\ndue to the syntax used in various programming languages,\n[\n7\n]\nalthough this can be confusing since\nFortran\nand\nPL\/I\nuse the syntax \"DO WHILE\" for pre-test loops.\n[\n8\n]\n[\n9\n]\nPost-test loops are commonly formatted in manner similar to\ndo\nbody\nrepeat\nwhile\ncondition\nInstead of the keywords\ndo\nand\nrepeat\nothers methods are sometime use to indicate where the\nbody\nbegins and ends, such as curly braces.\n[\n10\n]\nSome\nlanguages\nmay use a different naming convention for this type of loop. For example, the\nPascal\nand\nLua\nlanguages have a \"\nrepeat until\n\" loop, which continues to run\nuntil\nthe control expression is true and then terminates.\n[\n11\n]\n[\n12\n]\nThree-part for loop\n[\nedit\n]\nFlow diagram of a for loop that prints five asterisks.\nA\nthree-part for loop\n, popularized by C, has two additional parts:\ninitialization\n(\nloop variant\n),  and\nincrement\n, both of which are blocks of code. The\ninitialization\nis intended as code that prepares the loop and is run once in the beginning and\nincrement\nis used to update the state of the program after each iteration of the loop. Otherwise, the three-part for loop is a pre-test loop.\nThey are commonly formatted in manner similar to\nfor\ninitialization\n,\ncondition\n,\nincrement\ndo\nbody\nrepeat\nThis syntax came from\nB\nand was originally invented by\nStephen C. Johnson\n.\n[\n13\n]\nThe following C code is an example of a three part loop that prints the numbers from 0 to 4.\nfor\n(\nint\ni\n=\n0\n;\ni\n<\n5\n;\ni\n++\n)\n{\nprintf\n(\n\"%d\n\\n\n\"\n,\ni\n);\n}\nEquivalent constructs\n[\nedit\n]\nAssuming there is a function called\ndo_work()\nthat does some work, the following are equivalent.\n[\ncitation needed\n]\ndo\ndo_work()\nrepeat while\ncondition\ndo_work()\nwhile\ncondition\ndo\ndo_work()\nrepeat\nAs long as the\ncontinue\nstatement is not used, the above is technically equivalent to the following (though these examples are not typical or modern style used in everyday computers):\nwhile\ntrue\ndo\ndo_work()\nif\ncondition\nis not\ntrue\nthen\nbreak\nend if\nrepeat\nor\nLOOPSTART:\ndo_work()\nif\ncondition\nthen\ngoto\nLOOPSTART\nend if\nforeach\nloops are almost always used to iterate over items in a sequence of elements.\nAn\nenumeration\n(also known as an\ndeterminate loop\n[\n2\n]\n) is a loop intended to iterate over all the items of a collection.\n[\n14\n]\nIt is not as flexible as a conditional loop; but it is more predictable.\n[\ncitation needed\n]\nFor example, it is easier to guarantee that enumerations\nterminate\nand they avoid potential\noff-by-one errors\n.\n[\ncitation needed\n]\nEnumerations can be implemented using an\niterator\n, whether implicitly or explicitly. They are commonly formatted in manner similar to\nfor\nitem\nin\ncollection\nbody\nrepeat\nDepending on the programming language, various keywords are used to invoke enumerations. For example, descendants of\nALGOL\nuse\nfor\n,\n[\n15\n]\nwhile descendants of\nFortran\nuse\ndo\n[\n16\n]\nand\nCOBOL\nuses\nPERFORM VARYING\n.\n[\n17\n]\nEnumerations are sometimes called \"for loops,\" for example in\nZig\nand\nRust\n.\n[\n18\n]\n[\n19\n]\nThis can be confusing since many of the most popular\n[\n20\n]\nprogramming languages, such as C,\nC++\n, and\nJava\n, use that term for the three-part for loop,\n[\n21\n]\n[\n22\n]\n[\n23\n]\nwhich is not an enumeration. Other programming languages, such as\nPerl\nand\nC#\n, avoid this confusion by using the term \"foreach loop.\"\n[\n24\n]\n[\n25\n]\nThe order in which the items in the collection are iterated through depends on the programming language.\nFortran 95\nhas a loop, invoked using the keyword\nFORALL\n, that is independent of this order. It has the effect of executing each iteration of the loop at the same time. This feature was made obsolescent  in\nFortran 2018\n.\n[\n26\n]\nLoops in functional programming\n[\nedit\n]\nIn most\nfunctional programming languages\n,\nrecursion\nis used instead of traditional loops. This is due to the fact that variables are\nimmutable\n, and therefore the\nincrement\nstep of a loop cannot occur.\n[\n27\n]\nTo avoid running into\nstack overflow\nerrors for long loops, functional programming languages implement\ntail call optimisation\n, which allows the same\nstack frame\nto be used for each iteration of the loop, compiling to effectively the same code as a\nwhile\nor\nfor\nloop.\n[\n28\n]\nSome languages, such as\nHaskell\n, have a special syntax known as a\nlist comprehension\n, which is similar to enumeration, iterating over the contents of a list and transforming it into a new list.\nA\nloop counter\nis a control variable that controls the iterations of a loop. Loop counters change with each iteration of a loop, providing a unique value for each iteration. The loop counter is used to decide when the loop should terminate. It is so named because most uses of this construct result in the variable taking on a range of integer values.\nA common\nidentifier naming convention\nis for the loop counter to use the variable names\ni\n,\nj\n, and\nk\n(and so on if needed),\n[\n29\n]\nwhere\ni\nwould be the most outer loop,\nj\nthe next inner loop, etc. This style is generally agreed to have originated from the early programming of Fortran\n[\ncitation needed\n]\n, where these variable names beginning with these letters were implicitly declared as having an integer type, and so were obvious choices for loop counters that were only temporarily required. The practice dates back further to\nmathematical notation\nwhere\nindices\nfor\nsums\nand\nmultiplications\nare often\ni\n,\nj\n, and\nk\n.\nUsing terse names for loop counters, like\ni\nand\nj\n, is discouraged by some since the purpose of the variables is not as clear as if they were given a longer more descriptive name.\n[\n4\n]\n: 383–382 \nDifferent languages specify different rules for what value the loop counter will hold on termination of its loop, and indeed some hold that it becomes undefined. This permits a\ncompiler\nto generate code that leaves any value in the loop counter, or perhaps even leaves it unchanged because the loop value was held in a register and never stored in memory. Actual behavior may even vary according to the compiler's optimization settings.\nModifying the loop counter within the body of the loop can lead to unexpected consequences. To prevent such problems, some languages make the loop counter\nimmutable\n.\n[\ncitation needed\n]\nHowever, only overt changes are likely to be detected by the compiler. Situations where the address of the loop counter is passed as an argument to a\nsubroutine\n, make it very difficult to check because the routine's behavior is in general unknowable to the compiler unless the language supports procedure signatures and argument intents.\n[\ncitation needed\n]\nEarly exit and continuation\n[\nedit\n]\nSome languages may also provide supporting statements for altering how a loop's iteration proceeds. Common among these are the\nbreak\nstatement, which terminates the current loop the program is in, and the\ncontinue\nstatement, which skips to the next iteration of the current loop.\n[\n4\n]\n: 379 \nThese statements may have other names; For example in\nFortran 90\n, they are called\nexit\nand\ncycle\n.\n[\ncitation needed\n]\nA loop can also be terminated by\nreturning\nfrom the function within which it is being executed.\nIn the case of nested loops, the\nbreak\nand\ncontinue\nstatements apply to the inner most loop. Some languages allow loops to be labelled. These statements can then be applied to any of the loops in which the program is nested.\nouter_loop:\n(This is a label for the outermost loop)\nfor\n1 ≤ i ≤ 2\ndo\nfor\n1 ≤ j ≤ 2\ndo\ndisplay(i, j)\nif\ni = 2\ncontinue\nouter_loop\nend if\nrepeat\nrepeat\n(This nested loop displays the pairs (1, 1), (1, 2), and (2, 1))\nAn infinite loop is a loop which never terminates. This can be intentional, or the result of a\nlogic error\n.\nSystematically detecting infinite loops is known as the\nhalting problem\n.\n[\n30\n]\nInfinite loops are useful in applications which need to perform a repeated calculation until a program terminates, such as\nweb servers\n.\n[\n31\n]\nPrimitive recursive function\nGeneral recursive function\nRepeat loop (disambiguation)\nLOOP (programming language)\n– a programming language with the property that the functions it can compute are exactly the primitive recursive functions\n^\nAngelou, Alexandros; Dadaliaris, Antonios; Dossis, Michael; Dimitriou, Georgios (2021-11-26).\n\"Branchless Code Generation for Modern Processor Architectures\"\n.\n25th Pan-Hellenic Conference on Informatics\n. New York, NY, USA: ACM:\n300–\n305.\ndoi\n:\n10.1145\/3503823.3503879\n.\nISBN\n \n978-1-4503-9555-7\n.\n^\na\nb\nSamanta, Debasis; Sarma, Monalisa (15 June 2023).\nJoy with Java: Fundamentals of Object Oriented Programming\n. Cambridge University Press. p. 124.\nISBN\n \n978-1-009-21190-1\n.\n^\na\nb\n\"Conditional loops - Computational constructs - National 4 Computing Science Revision\"\n.\nBBC Bitesize\n. Archived from\nthe original\non 19 October 2021\n. Retrieved\n8 January\n2026\n.\n^\na\nb\nc\nd\nMcConnell, Steve (9 June 2004).\nCode Complete\n. Pearson Education.\nISBN\n \n978-0-7356-3697-2\n.\n^\n\"while Statement (GNU C Language Manual)\"\n.\nwww.gnu.org\n. Archived from\nthe original\non 12 July 2024\n. Retrieved\n8 January\n2026\n.\n^\n\"3. An Informal Introduction to Python\"\n.\nPython documentation\n. Archived from\nthe original\non 31 December 2025\n. Retrieved\n8 January\n2026\n.\n^\n\"do...while - JavaScript | MDN\"\n.\nMDN Web Docs\n. 2025-07-08\n. Retrieved\n2026-01-22\n.\n^\n\"DO WHILE (FORTRAN 77 Language Reference)\"\n.\ndocs.oracle.com\n. Archived from\nthe original\non 14 March 2023\n. Retrieved\n8 January\n2026\n.\n^\n\"DO command (PL\/I)\"\n.\nwww.ibm.com\n. Archived from\nthe original\non 2 March 2025\n. Retrieved\n22 January\n2026\n.\n^\n\"do-while Statement (GNU C Language Manual)\"\n.\nwww.gnu.org\n. Archived from\nthe original\non 13 July 2024\n. Retrieved\n8 January\n2026\n.\n^\n\"The Repeat..until statement\"\n.\nwww.freepascal.org\n. Archived from\nthe original\non 9 November 2025\n. Retrieved\n22 January\n2026\n.\n^\n\"Programming in Lua : 4.3.3\"\n.\nwww.lua.org\n. Archived from\nthe original\non 2 January 2026\n. Retrieved\n22 January\n2026\n.\n^\nThompson, Ken\n.\nVCF East 2019 – Brian Kernighan interviews Ken Thompson\n.\nYouTube\n.\nArchived\nfrom the original on 2021-12-12\n. Retrieved\n2020-11-16\n.\nI saw Johnson's semicolon version of the for loop and I put that in [B], I stole it.\n^\nMcConnell, Steve (9 June 2004).\nCode Complete\n. Pearson Education. p. 367.\nISBN\n \n978-0-7356-3697-2\n.\n^\nWirth, Niklaus\n(1973). \"Preface\".\nSystematic Programming: An Introduction\n. Prentice-Hall. pp. xiii.\nISBN\n \n0138803692\n.\n^\n\"DO \/ END DO\"\n.\nwww.ibm.com\n. 24 April 2018. Archived from\nthe original\non 8 January 2026\n. Retrieved\n8 January\n2026\n.\n^\n\"PERFORM with VARYING Phrase\"\n.\nwww.ibm.com\n. June 2012. Archived from\nthe original\non 8 January 2026\n. Retrieved\n8 January\n2026\n.\n^\n\"Zig documentation\"\n.\nziglang.org\n. Archived from\nthe original\non 4 January 2026\n. Retrieved\n8 January\n2026\n.\n^\n\"Looping Through a Collection with for\"\n.\nrust-lang.org\n. Archived from\nthe original\non 19 December 2025\n. Retrieved\n8 January\n2026\n.\n^\n\"TIOBE Index for September 2024\"\n. Archived from\nthe original\non January 4, 2026\n. Retrieved\n2025-12-16\n.\n^\n\"for Statement (GNU C Language Manual)\"\n.\nwww.gnu.org\n. Archived from\nthe original\non 13 July 2024\n. Retrieved\n8 January\n2026\n.\n^\n\"for statement (C++)\"\n.\nlearn.microsoft.com\n. Archived from\nthe original\non 28 September 2025\n. Retrieved\n8 January\n2026\n.\n^\n\"The for Statement (The Java™ Tutorials > Learning the Java Language > Language Basics)\"\n.\ndocs.oracle.com\n. Archived from\nthe original\non 28 December 2025\n. Retrieved\n8 January\n2026\n.\n^\n\"Iteration statements -for, foreach, do, and while - C# reference\"\n.\nlearn.microsoft.com\n. Archived from\nthe original\non 28 December 2025\n. Retrieved\n8 January\n2026\n.\n^\n\"Perl for Loop\"\n.\nPerl Tutorial\n. Archived from\nthe original\non 7 June 2025\n. Retrieved\n8 January\n2026\n.\n^\n\"FORALL\"\n.\nIntel\n. Archived from\nthe original\non 1 January 2026\n. Retrieved\n8 January\n2026\n.\n^\nHinsen, Konrad (2009).\n\"The Promises of Functional Programming\"\n.\nComputing in Science & Engineering\n.\n11\n(4):\n86–\n90.\nBibcode\n:\n2009CSE....11d..86H\n.\ndoi\n:\n10.1109\/mcse.2009.129\n.\nISSN\n \n1521-9615\n.\n^\nClinger, William D. (1998). \"Proper tail recursion and space efficiency\".\nProceedings of the ACM SIGPLAN 1998 conference on Programming language design and implementation\n. New York, NY, USA: ACM. pp. \n174–\n185.\ndoi\n:\n10.1145\/277650.277719\n.\nISBN\n \n0-89791-987-4\n.\n^\nhttp:\/\/www.knosof.co.uk\/vulnerabilities\/loopcntrl.pdf\nAnalysis of loop control variables in C\n^\nLee, Sarah.\n\"Turing's Halting Problem Explained\"\n.\nwww.numberanalytics.com\n. Retrieved\n2026-01-22\n.\n^\n\"What is an infinite loop (endless loop)?\"\n.\nWhatIs\n. Retrieved\n2026-01-22\n.","attrs_markdown":"[Jump to content](https:\/\/en.wikipedia.org\/wiki\/While_loop#bodyContent)\n\nMain menu\n\nMain menu\n\nmove to sidebar\n\nhide\n\nNavigation\n\n- [Main page](https:\/\/en.wikipedia.org\/wiki\/Main_Page \"Visit the main page [z]\")\n- [Contents](https:\/\/en.wikipedia.org\/wiki\/Wikipedia:Contents \"Guides to browsing Wikipedia\")\n- [Current events](https:\/\/en.wikipedia.org\/wiki\/Portal:Current_events \"Articles related to current events\")\n- [Random article](https:\/\/en.wikipedia.org\/wiki\/Special:Random \"Visit a randomly selected article [x]\")\n- [About Wikipedia](https:\/\/en.wikipedia.org\/wiki\/Wikipedia:About \"Learn about Wikipedia and how it works\")\n- [Contact us](https:\/\/en.wikipedia.org\/wiki\/Wikipedia:Contact_us \"How to contact Wikipedia\")\n\nContribute\n\n- [Help](https:\/\/en.wikipedia.org\/wiki\/Help:Contents \"Guidance on how to use and edit Wikipedia\")\n- [Learn to edit](https:\/\/en.wikipedia.org\/wiki\/Help:Introduction \"Learn how to edit Wikipedia\")\n- [Community portal](https:\/\/en.wikipedia.org\/wiki\/Wikipedia:Community_portal \"The hub for editors\")\n- [Recent changes](https:\/\/en.wikipedia.org\/wiki\/Special:RecentChanges \"A list of recent changes to Wikipedia [r]\")\n- [Upload file](https:\/\/en.wikipedia.org\/wiki\/Wikipedia:File_upload_wizard \"Add images or other media for use on Wikipedia\")\n- [Special pages](https:\/\/en.wikipedia.org\/wiki\/Special:SpecialPages \"A list of all special pages [q]\")\n\n[![](https:\/\/en.wikipedia.org\/static\/images\/icons\/enwiki-25.svg) ![Wikipedia](https:\/\/en.wikipedia.org\/static\/images\/mobile\/copyright\/wikipedia-wordmark-en-25.svg) ![The Free Encyclopedia](https:\/\/en.wikipedia.org\/static\/images\/mobile\/copyright\/wikipedia-tagline-en-25.svg)](https:\/\/en.wikipedia.org\/wiki\/Main_Page)\n\n[Search](https:\/\/en.wikipedia.org\/wiki\/Special:Search \"Search Wikipedia [f]\")\n\nAppearance\n\n- [Donate](https:\/\/donate.wikimedia.org\/?wmf_source=donate&wmf_medium=sidebar&wmf_campaign=en.wikipedia.org&uselang=en)\n- [Create account](https:\/\/en.wikipedia.org\/w\/index.php?title=Special:CreateAccount&returnto=Loop+%28statement%29 \"You are encouraged to create an account and log in; however, it is not mandatory\")\n- [Log in](https:\/\/en.wikipedia.org\/w\/index.php?title=Special:UserLogin&returnto=Loop+%28statement%29 \"You're encouraged to log in; however, it's not mandatory. [o]\")\n\nPersonal tools\n\n- [Donate](https:\/\/donate.wikimedia.org\/?wmf_source=donate&wmf_medium=sidebar&wmf_campaign=en.wikipedia.org&uselang=en)\n- [Create account](https:\/\/en.wikipedia.org\/w\/index.php?title=Special:CreateAccount&returnto=Loop+%28statement%29 \"You are encouraged to create an account and log in; however, it is not mandatory\")\n- [Log in](https:\/\/en.wikipedia.org\/w\/index.php?title=Special:UserLogin&returnto=Loop+%28statement%29 \"You're encouraged to log in; however, it's not mandatory. [o]\")\n\n## Contents\nmove to sidebar\n\nhide\n\n- [(Top)](https:\/\/en.wikipedia.org\/wiki\/While_loop)\n- [1 Overview](https:\/\/en.wikipedia.org\/wiki\/While_loop#Overview)\n- [2 Conditional loop](https:\/\/en.wikipedia.org\/wiki\/While_loop#Conditional_loop)\n  Toggle Conditional loop subsection\n  - [2\\.1 Pre-test loop](https:\/\/en.wikipedia.org\/wiki\/While_loop#Pre-test_loop)\n  - [2\\.2 Post-test loop](https:\/\/en.wikipedia.org\/wiki\/While_loop#Post-test_loop)\n  - [2\\.3 Three-part for loop](https:\/\/en.wikipedia.org\/wiki\/While_loop#Three-part_for_loop)\n  - [2\\.4 Equivalent constructs](https:\/\/en.wikipedia.org\/wiki\/While_loop#Equivalent_constructs)\n- [3 Enumeration](https:\/\/en.wikipedia.org\/wiki\/While_loop#Enumeration)\n- [4 Loops in functional programming](https:\/\/en.wikipedia.org\/wiki\/While_loop#Loops_in_functional_programming)\n- [5 Loop counter](https:\/\/en.wikipedia.org\/wiki\/While_loop#Loop_counter)\n- [6 Early exit and continuation](https:\/\/en.wikipedia.org\/wiki\/While_loop#Early_exit_and_continuation)\n- [7 Infinite loop](https:\/\/en.wikipedia.org\/wiki\/While_loop#Infinite_loop)\n- [8 See also](https:\/\/en.wikipedia.org\/wiki\/While_loop#See_also)\n- [9 References](https:\/\/en.wikipedia.org\/wiki\/While_loop#References)\n\nToggle the table of contents\n\n# Loop (statement)\n25 languages\n\n- [Boarisch](https:\/\/bar.wikipedia.org\/wiki\/Schleifn_\\(Programmierung\\) \"Schleifn (Programmierung) – Bavarian\")\n- [Български](https:\/\/bg.wikipedia.org\/wiki\/%D0%A6%D0%B8%D0%BA%D1%8A%D0%BB_\\(%D0%BF%D1%80%D0%BE%D0%B3%D1%80%D0%B0%D0%BC%D0%B8%D1%80%D0%B0%D0%BD%D0%B5\\) \"Цикъл (програмиране) – Bulgarian\")\n- [Català](https:\/\/ca.wikipedia.org\/wiki\/Bucle_\\(programaci%C3%B3\\) \"Bucle (programació) – Catalan\")\n- [Deutsch](https:\/\/de.wikipedia.org\/wiki\/Schleife_\\(Programmierung\\) \"Schleife (Programmierung) – German\")\n- [Español](https:\/\/es.wikipedia.org\/wiki\/Bucle_\\(programaci%C3%B3n\\) \"Bucle (programación) – Spanish\")\n- [Eesti](https:\/\/et.wikipedia.org\/wiki\/Ts%C3%BCkkel_\\(programmeerimine\\) \"Tsükkel (programmeerimine) – Estonian\")\n- [Euskara](https:\/\/eu.wikipedia.org\/wiki\/Begizta_\\(programazioa\\) \"Begizta (programazioa) – Basque\")\n- [Suomi](https:\/\/fi.wikipedia.org\/wiki\/Toistorakenne \"Toistorakenne – Finnish\")\n- [Gaeilge](https:\/\/ga.wikipedia.org\/wiki\/L%C3%BAb \"Lúb – Irish\")\n- [עברית](https:\/\/he.wikipedia.org\/wiki\/%D7%9C%D7%95%D7%9C%D7%90%D7%94_\\(%D7%AA%D7%9B%D7%A0%D7%95%D7%AA\\) \"לולאה (תכנות) – Hebrew\")\n- [Magyar](https:\/\/hu.wikipedia.org\/wiki\/Ciklus_\\(programoz%C3%A1s\\) \"Ciklus (programozás) – Hungarian\")\n- [Italiano](https:\/\/it.wikipedia.org\/wiki\/Ciclo_\\(informatica\\) \"Ciclo (informatica) – Italian\")\n- [日本語](https:\/\/ja.wikipedia.org\/wiki\/%E3%83%AB%E3%83%BC%E3%83%97_\\(%E3%83%97%E3%83%AD%E3%82%B0%E3%83%A9%E3%83%9F%E3%83%B3%E3%82%B0\\) \"ループ (プログラミング) – Japanese\")\n- [Қазақша](https:\/\/kk.wikipedia.org\/wiki\/%D0%A6%D0%B8%D0%BA%D0%BB_\\(%D0%B8%D0%BD%D1%84%D0%BE%D1%80%D0%BC%D0%B0%D1%82%D0%B8%D0%BA%D0%B0\\) \"Цикл (информатика) – Kazakh\")\n- [Latviešu](https:\/\/lv.wikipedia.org\/wiki\/Cikls_\\(programm%C4%93%C5%A1ana\\) \"Cikls (programmēšana) – Latvian\")\n- [Олык марий](https:\/\/mhr.wikipedia.org\/wiki\/%D0%A6%D0%B8%D0%BA%D0%BB \"Цикл – Eastern Mari\")\n- [Nederlands](https:\/\/nl.wikipedia.org\/wiki\/Repetitie_\\(informatica\\) \"Repetitie (informatica) – Dutch\")\n- [Polski](https:\/\/pl.wikipedia.org\/wiki\/P%C4%99tla_\\(informatyka\\) \"Pętla (informatyka) – Polish\")\n- [Português](https:\/\/pt.wikipedia.org\/wiki\/Estrutura_de_repeti%C3%A7%C3%A3o \"Estrutura de repetição – Portuguese\")\n- [Русский](https:\/\/ru.wikipedia.org\/wiki\/%D0%A6%D0%B8%D0%BA%D0%BB_\\(%D0%BF%D1%80%D0%BE%D0%B3%D1%80%D0%B0%D0%BC%D0%BC%D0%B8%D1%80%D0%BE%D0%B2%D0%B0%D0%BD%D0%B8%D0%B5\\) \"Цикл (программирование) – Russian\")\n- [Српски \/ srpski](https:\/\/sr.wikipedia.org\/wiki\/Ra%C4%8Dunarska_petlja \"Računarska petlja – Serbian\")\n- [Svenska](https:\/\/sv.wikipedia.org\/wiki\/Loop_\\(programmering\\) \"Loop (programmering) – Swedish\")\n- [Українська](https:\/\/uk.wikipedia.org\/wiki\/%D0%A6%D0%B8%D0%BA%D0%BB_\\(%D0%BF%D1%80%D0%BE%D0%B3%D1%80%D0%B0%D0%BC%D1%83%D0%B2%D0%B0%D0%BD%D0%BD%D1%8F\\) \"Цикл (програмування) – Ukrainian\")\n- [粵語](https:\/\/zh-yue.wikipedia.org\/wiki\/%E8%BF%B4%E5%9C%88 \"迴圈 – Cantonese\")\n- [中文](https:\/\/zh.wikipedia.org\/wiki\/%E8%BF%B4%E5%9C%88 \"迴圈 – Chinese\")\n\n[Edit links](https:\/\/www.wikidata.org\/wiki\/Special:EntityPage\/Q8868615#sitelinks-wikipedia \"Edit interlanguage links\")\n\n- [Article](https:\/\/en.wikipedia.org\/wiki\/Loop_\\(statement\\) \"View the content page [c]\")\n- [Talk](https:\/\/en.wikipedia.org\/wiki\/Talk:Loop_\\(statement\\) \"Discuss improvements to the content page [t]\")\n\nEnglish\n\n- [Read](https:\/\/en.wikipedia.org\/wiki\/Loop_\\(statement\\))\n- [Edit](https:\/\/en.wikipedia.org\/w\/index.php?title=Loop_\\(statement\\)&action=edit \"Edit this page [e]\")\n- [View history](https:\/\/en.wikipedia.org\/w\/index.php?title=Loop_\\(statement\\)&action=history \"Past revisions of this page [h]\")\n\nTools\n\nTools\n\nmove to sidebar\n\nhide\n\nActions\n\n- [Read](https:\/\/en.wikipedia.org\/wiki\/Loop_\\(statement\\))\n- [Edit](https:\/\/en.wikipedia.org\/w\/index.php?title=Loop_\\(statement\\)&action=edit \"Edit this page [e]\")\n- [View history](https:\/\/en.wikipedia.org\/w\/index.php?title=Loop_\\(statement\\)&action=history)\n\nGeneral\n\n- [What links here](https:\/\/en.wikipedia.org\/wiki\/Special:WhatLinksHere\/Loop_\\(statement\\) \"List of all English Wikipedia pages containing links to this page 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PDF](https:\/\/en.wikipedia.org\/w\/index.php?title=Special:DownloadAsPdf&page=Loop_%28statement%29&action=show-download-screen \"Download this page as a PDF file\")\n- [Printable version](https:\/\/en.wikipedia.org\/w\/index.php?title=Loop_\\(statement\\)&printable=yes \"Printable version of this page [p]\")\n\nIn other projects\n\n- [Wikimedia Commons](https:\/\/commons.wikimedia.org\/wiki\/Category:Programming_loops)\n- [Wikidata item](https:\/\/www.wikidata.org\/wiki\/Special:EntityPage\/Q8868615 \"Structured data on this page hosted by Wikidata [g]\")\n\nAppearance\n\nmove to sidebar\n\nhide\n\nFrom Wikipedia, the free encyclopedia\n\n(Redirected from [While loop](https:\/\/en.wikipedia.org\/w\/index.php?title=While_loop&redirect=no \"While loop\"))\n\nControl flow statement for executing code repeatedly\n\n|   |   |\n|---|---|\n| [![icon](https:\/\/upload.wikimedia.org\/wikipedia\/en\/thumb\/9\/99\/Question_book-new.svg\/60px-Question_book-new.svg.png)](https:\/\/en.wikipedia.org\/wiki\/File:Question_book-new.svg) | This article **needs additional citations for [verification](https:\/\/en.wikipedia.org\/wiki\/Wikipedia:Verifiability \"Wikipedia:Verifiability\")**. Please help [improve this article](https:\/\/en.wikipedia.org\/wiki\/Special:EditPage\/Loop_\\(statement\\) \"Special:EditPage\/Loop (statement)\") by [adding citations to reliable sources](https:\/\/en.wikipedia.org\/wiki\/Help:Referencing_for_beginners \"Help:Referencing for beginners\"). Unsourced material may be challenged and removed. *Find sources:* [\"Loop\" statement](https:\/\/www.google.com\/search?as_eq=wikipedia&q=%22Loop%22+statement) – [news](https:\/\/www.google.com\/search?tbm=nws&q=%22Loop%22+statement+-wikipedia&tbs=ar:1) **·** [newspapers](https:\/\/www.google.com\/search?&q=%22Loop%22+statement&tbs=bkt:s&tbm=bks) **·** [books](https:\/\/www.google.com\/search?tbs=bks:1&q=%22Loop%22+statement+-wikipedia) **·** [scholar](https:\/\/scholar.google.com\/scholar?q=%22Loop%22+statement) **·** [JSTOR](https:\/\/www.jstor.org\/action\/doBasicSearch?Query=%22Loop%22+statement&acc=on&wc=on) *(January 2026)* *([Learn how and when to remove this message](https:\/\/en.wikipedia.org\/wiki\/Help:Maintenance_template_removal \"Help:Maintenance template removal\"))* |\n\nIn [computer programming](https:\/\/en.wikipedia.org\/wiki\/Computer_programming \"Computer programming\"), a **loop** is a [control flow](https:\/\/en.wikipedia.org\/wiki\/Control_flow \"Control flow\") [statement](https:\/\/en.wikipedia.org\/wiki\/Statement_\\(computer_science\\) \"Statement (computer science)\") that allows code to be executed repeatedly, usually with minor alterations between repetitions. Loops can be used to perform a repeated action on all items in a [collection](https:\/\/en.wikipedia.org\/wiki\/Collection_\\(abstract_data_type\\) \"Collection (abstract data type)\"), or to implement a long lived program.\n\n## Overview\n\\[[edit](https:\/\/en.wikipedia.org\/w\/index.php?title=Loop_\\(statement\\)&action=edit&section=1 \"Edit section: Overview\")\\]\n\nLoops are a feature of [high-level programming languages](https:\/\/en.wikipedia.org\/wiki\/High-level_programming_languages \"High-level programming languages\"). In [low-level programming languages](https:\/\/en.wikipedia.org\/wiki\/Low-level_programming_languages \"Low-level programming languages\") the same functionality is achieved using [jumps](https:\/\/en.wikipedia.org\/wiki\/Control_flow#Jump \"Control flow\"). When a program is [compiled](https:\/\/en.wikipedia.org\/wiki\/Compiler \"Compiler\") to [machine code](https:\/\/en.wikipedia.org\/wiki\/Machine_code \"Machine code\"), looping may be achieved using jumps; but some loops can be [optimized](https:\/\/en.wikipedia.org\/wiki\/Code_optimization \"Code optimization\") to run without jumping.[\\[1\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-1)\n\nUsually, loops are expected to run for a finite number of iteration.\\[*[citation needed](https:\/\/en.wikipedia.org\/wiki\/Wikipedia:Citation_needed \"Wikipedia:Citation needed\")*\\] Without proper care, loops may accidentally be created that have no possibility of terminating. Such loops are called [infinite loops](https:\/\/en.wikipedia.org\/wiki\/Infinite_loop \"Infinite loop\"). The problem of determining whether a program contains an infinite loop is known as the [halting problem](https:\/\/en.wikipedia.org\/wiki\/Halting_problem \"Halting problem\").\n\n## Conditional loop\n\\[[edit](https:\/\/en.wikipedia.org\/w\/index.php?title=Loop_\\(statement\\)&action=edit&section=2 \"Edit section: Conditional loop\")\\]\n\nA **conditional loop** (also known as an **indeterminate loop**[\\[2\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-joy-2)) is a loop that determines whether to terminate based on a logical condition.[\\[3\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-bbc1-3) These loops are flexible, but there exact behavior can be difficult to reason about.[\\[4\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-codecomplete-4): 368\n\nA conditional loop is usually composed of two parts: a *condition* and a *body*. The *condition* is a logical statement depending on the state of the program and the *body* is a block of code that runs as long as the *condition* holds.[\\[3\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-bbc1-3)\n\nA common misconception is that the execution of the *body* terminates as soon as the *condition* does not hold anymore; but this is usually not the case.[\\[4\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-codecomplete-4): 368  In most programming languages, the *condition* is checked once for every execution of the *body*. When the *condition* is checked is not standardized and some programming languages contain multiple conditional looping structures with different rules about when the *condition* is assessed.\\[*[citation needed](https:\/\/en.wikipedia.org\/wiki\/Wikipedia:Citation_needed \"Wikipedia:Citation needed\")*\\]\n\n### Pre-test loop\n\\[[edit](https:\/\/en.wikipedia.org\/w\/index.php?title=Loop_\\(statement\\)&action=edit&section=3 \"Edit section: Pre-test loop\")\\]\n\nA **pre-test loop** is a conditional loop where the *condition* is checked before the *body* is executed. More precisely, the *condition* is checked and if it holds the *body* is execute. Afterwards, the *condition* is checked again, and if it holds the *body* is executed again. This process repeats until the *condition* does not hold. Many programming languages call this loop a *while loop* and refer to it with the [keyword](https:\/\/en.wikipedia.org\/wiki\/Reserved_word \"Reserved word\") *while*. They are commonly formatted in manner similar to\n```\nwhile condition do\n    body\nrepeat\n```\nInstead of the keywords *do* and *repeat* others methods are sometime use to indicate where the *body* begins and ends, such as [curly braces](https:\/\/en.wikipedia.org\/wiki\/Curly_braces \"Curly braces\")[\\[5\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-5) or [whitespace](https:\/\/en.wikipedia.org\/wiki\/Whitespace_characters \"Whitespace characters\").[\\[6\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-6)\n\nFor example, the following code fragment first checks whether *x* is less than five, which it is, so the *body* is entered. There, *x* is displayed and then incremented by one. After executing the statements in the *body*, the *condition* is checked again, and the loop is executed again. This process repeats until *x* has the value five.\n```\nx ← 0\nwhile x < 5 do\n    display(x)\n    x ← x + 1\nrepeat\n```\n### Post-test loop\n\\[[edit](https:\/\/en.wikipedia.org\/w\/index.php?title=Loop_\\(statement\\)&action=edit&section=4 \"Edit section: Post-test loop\")\\]\n\n[![](https:\/\/upload.wikimedia.org\/wikipedia\/commons\/thumb\/9\/92\/Do-while-loop-diagram.svg\/250px-Do-while-loop-diagram.svg.png)](https:\/\/en.wikipedia.org\/wiki\/File:Do-while-loop-diagram.svg)\n\nDo-While loop flow diagram\n\nA **post-test loop** is a conditional loop where the *condition* is checked after the *body* is executed. More precisely, the *body* is executed and afterwards the *condition* is checked. If it holds the *body* is run again and then the *condition* is checked. This is repeated until the *condition* does not hold. This is sometimes called a *do-while loop* due to the syntax used in various programming languages,[\\[7\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-7) although this can be confusing since [Fortran](https:\/\/en.wikipedia.org\/wiki\/Fortran \"Fortran\") and [PL\/I](https:\/\/en.wikipedia.org\/wiki\/PL\/I \"PL\/I\") use the syntax \"DO WHILE\" for pre-test loops.[\\[8\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-8)[\\[9\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-9) Post-test loops are commonly formatted in manner similar to\n```\ndo\n    body\nrepeat while condition\n```\nInstead of the keywords *do* and *repeat* others methods are sometime use to indicate where the *body* begins and ends, such as curly braces.[\\[10\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-10)\n\nSome [languages](https:\/\/en.wikipedia.org\/wiki\/Programming_language \"Programming language\") may use a different naming convention for this type of loop. For example, the [Pascal](https:\/\/en.wikipedia.org\/wiki\/Pascal_programming_language \"Pascal programming language\") and [Lua](https:\/\/en.wikipedia.org\/wiki\/Lua_\\(programming_language\\) \"Lua (programming language)\") languages have a \"*repeat until*\" loop, which continues to run *until* the control expression is true and then terminates.[\\[11\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-11)[\\[12\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-12)\n\n### Three-part for loop\n\\[[edit](https:\/\/en.wikipedia.org\/w\/index.php?title=Loop_\\(statement\\)&action=edit&section=5 \"Edit section: Three-part for loop\")\\]\n\n[![](https:\/\/upload.wikimedia.org\/wikipedia\/commons\/thumb\/d\/d1\/For_loop_example.svg\/250px-For_loop_example.svg.png)](https:\/\/en.wikipedia.org\/wiki\/File:For_loop_example.svg)\n\nFlow diagram of a for loop that prints five asterisks.\n\nA **three-part for loop**, popularized by C, has two additional parts: [*initialization*](https:\/\/en.wikipedia.org\/wiki\/Declaration_\\(computer_programming\\) \"Declaration (computer programming)\") ([loop variant](https:\/\/en.wikipedia.org\/wiki\/Loop_variant \"Loop variant\")), and *increment*, both of which are blocks of code. The *initialization* is intended as code that prepares the loop and is run once in the beginning and *increment* is used to update the state of the program after each iteration of the loop. Otherwise, the three-part for loop is a pre-test loop. They are commonly formatted in manner similar to\n```\nfor initialization, condition, increment do\n    body\nrepeat\n```\nThis syntax came from [B](https:\/\/en.wikipedia.org\/wiki\/B_\\(programming_language\\) \"B (programming language)\") and was originally invented by [Stephen C. Johnson](https:\/\/en.wikipedia.org\/wiki\/Stephen_C._Johnson \"Stephen C. Johnson\").[\\[13\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-ken-13) The following C code is an example of a three part loop that prints the numbers from 0 to 4.\n```\nfor (int i = 0; i < 5; i++) {\n    printf(\"%d\\n\", i);\n}\n```\n### Equivalent constructs\n\\[[edit](https:\/\/en.wikipedia.org\/w\/index.php?title=Loop_\\(statement\\)&action=edit&section=6 \"Edit section: Equivalent constructs\")\\]\n\n|   |   |\n|---|---|\n| [![\\[icon\\]](https:\/\/upload.wikimedia.org\/wikipedia\/commons\/thumb\/1\/1c\/Wiki_letter_w_cropped.svg\/20px-Wiki_letter_w_cropped.svg.png)](https:\/\/en.wikipedia.org\/wiki\/File:Wiki_letter_w_cropped.svg) | This section **needs expansion**. You can help by [adding missing information](https:\/\/en.wikipedia.org\/w\/index.php?title=Loop_\\(statement\\)&action=edit&section=). *(January 2026)* |\n\nAssuming there is a function called *do\\_work()* that does some work, the following are equivalent.\\[*[citation needed](https:\/\/en.wikipedia.org\/wiki\/Wikipedia:Citation_needed \"Wikipedia:Citation needed\")*\\]\n\nAs long as the *continue* statement is not used, the above is technically equivalent to the following (though these examples are not typical or modern style used in everyday computers):\n```\nwhile true do\n    do_work()\n    if condition is not true then\n        break\n    end if\nrepeat\n```\nor\n```\nLOOPSTART:\ndo_work()\nif condition then\n    goto LOOPSTART\nend if\n```\n## Enumeration\n\\[[edit](https:\/\/en.wikipedia.org\/w\/index.php?title=Loop_\\(statement\\)&action=edit&section=7 \"Edit section: Enumeration\")\\]\n\n[![](https:\/\/upload.wikimedia.org\/wikipedia\/commons\/thumb\/1\/13\/For-Loop-Mint-Programming-Language-Type-2.gif\/250px-For-Loop-Mint-Programming-Language-Type-2.gif)](https:\/\/en.wikipedia.org\/wiki\/File:For-Loop-Mint-Programming-Language-Type-2.gif)\n\n`foreach` loops are almost always used to iterate over items in a sequence of elements.\n\nAn **enumeration** (also known as an **determinate loop**[\\[2\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-joy-2)) is a loop intended to iterate over all the items of a collection.[\\[14\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-14) It is not as flexible as a conditional loop; but it is more predictable.\\[*[citation needed](https:\/\/en.wikipedia.org\/wiki\/Wikipedia:Citation_needed \"Wikipedia:Citation needed\")*\\] For example, it is easier to guarantee that enumerations [terminate](https:\/\/en.wikipedia.org\/wiki\/Terminate \"Terminate\") and they avoid potential [off-by-one errors](https:\/\/en.wikipedia.org\/wiki\/Off-by-one_error \"Off-by-one error\").\\[*[citation needed](https:\/\/en.wikipedia.org\/wiki\/Wikipedia:Citation_needed \"Wikipedia:Citation needed\")*\\] Enumerations can be implemented using an [iterator](https:\/\/en.wikipedia.org\/wiki\/Iterator \"Iterator\"), whether implicitly or explicitly. They are commonly formatted in manner similar to\n```\nfor item in collection\n    body\nrepeat\n```\nDepending on the programming language, various keywords are used to invoke enumerations. For example, descendants of [ALGOL](https:\/\/en.wikipedia.org\/wiki\/ALGOL \"ALGOL\") use `for`,[\\[15\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-15) while descendants of [Fortran](https:\/\/en.wikipedia.org\/wiki\/Fortran \"Fortran\") use `do`[\\[16\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-16) and [COBOL](https:\/\/en.wikipedia.org\/wiki\/COBOL \"COBOL\") uses `PERFORM VARYING`.[\\[17\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-17)\n\nEnumerations are sometimes called \"for loops,\" for example in [Zig](https:\/\/en.wikipedia.org\/wiki\/Zig_\\(programming_language\\) \"Zig (programming language)\") and [Rust](https:\/\/en.wikipedia.org\/wiki\/Rust_\\(programming_language\\) \"Rust (programming language)\").[\\[18\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-18)[\\[19\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-19) This can be confusing since many of the most popular[\\[20\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-20) programming languages, such as C, [C++](https:\/\/en.wikipedia.org\/wiki\/C%2B%2B \"C++\"), and [Java](https:\/\/en.wikipedia.org\/wiki\/Java_\\(programming_language\\) \"Java (programming language)\"), use that term for the three-part for loop,[\\[21\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-21)[\\[22\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-22)[\\[23\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-23) which is not an enumeration. Other programming languages, such as [Perl](https:\/\/en.wikipedia.org\/wiki\/Perl \"Perl\") and [C\\#](https:\/\/en.wikipedia.org\/wiki\/C \"C\"), avoid this confusion by using the term \"foreach loop.\"[\\[24\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-24)[\\[25\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-25)\n\nThe order in which the items in the collection are iterated through depends on the programming language. [Fortran 95](https:\/\/en.wikipedia.org\/wiki\/Fortran_95 \"Fortran 95\") has a loop, invoked using the keyword `FORALL`, that is independent of this order. It has the effect of executing each iteration of the loop at the same time. This feature was made obsolescent in [Fortran 2018](https:\/\/en.wikipedia.org\/wiki\/Fortran_2018 \"Fortran 2018\").[\\[26\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-26)\n\n## Loops in functional programming\n\\[[edit](https:\/\/en.wikipedia.org\/w\/index.php?title=Loop_\\(statement\\)&action=edit&section=8 \"Edit section: Loops in functional programming\")\\]\n\n|   |   |\n|---|---|\n| [![\\[icon\\]](https:\/\/upload.wikimedia.org\/wikipedia\/commons\/thumb\/1\/1c\/Wiki_letter_w_cropped.svg\/20px-Wiki_letter_w_cropped.svg.png)](https:\/\/en.wikipedia.org\/wiki\/File:Wiki_letter_w_cropped.svg) | This section **needs expansion**. You can help by [adding missing information](https:\/\/en.wikipedia.org\/w\/index.php?title=Loop_\\(statement\\)&action=edit&section=). *(January 2026)* |\n\nIn most [functional programming languages](https:\/\/en.wikipedia.org\/wiki\/Functional_programming \"Functional programming\"), [recursion](https:\/\/en.wikipedia.org\/wiki\/Recursion_\\(computer_science\\) \"Recursion (computer science)\") is used instead of traditional loops. This is due to the fact that variables are [immutable](https:\/\/en.wikipedia.org\/wiki\/Immutable_object \"Immutable object\"), and therefore the *increment* step of a loop cannot occur.[\\[27\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-27)\n\nTo avoid running into [stack overflow](https:\/\/en.wikipedia.org\/wiki\/Stack_overflow \"Stack overflow\") errors for long loops, functional programming languages implement [tail call optimisation](https:\/\/en.wikipedia.org\/wiki\/Tail_call \"Tail call\"), which allows the same [stack frame](https:\/\/en.wikipedia.org\/wiki\/Call_stack \"Call stack\") to be used for each iteration of the loop, compiling to effectively the same code as a *while* or *for* loop.[\\[28\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-28)\n\nSome languages, such as [Haskell](https:\/\/en.wikipedia.org\/wiki\/Haskell \"Haskell\"), have a special syntax known as a [list comprehension](https:\/\/en.wikipedia.org\/wiki\/List_comprehension \"List comprehension\"), which is similar to enumeration, iterating over the contents of a list and transforming it into a new list.\n\n## Loop counter\n\\[[edit](https:\/\/en.wikipedia.org\/w\/index.php?title=Loop_\\(statement\\)&action=edit&section=9 \"Edit section: Loop counter\")\\]\n\nA  **loop counter** is a control variable that controls the iterations of a loop. Loop counters change with each iteration of a loop, providing a unique value for each iteration. The loop counter is used to decide when the loop should terminate. It is so named because most uses of this construct result in the variable taking on a range of integer values.\n\nA common [identifier naming convention](https:\/\/en.wikipedia.org\/wiki\/Identifier_naming_convention \"Identifier naming convention\") is for the loop counter to use the variable names *i*, *j*, and *k* (and so on if needed),[\\[29\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-29) where *i* would be the most outer loop, *j* the next inner loop, etc. This style is generally agreed to have originated from the early programming of Fortran\\[*[citation needed](https:\/\/en.wikipedia.org\/wiki\/Wikipedia:Citation_needed \"Wikipedia:Citation needed\")*\\], where these variable names beginning with these letters were implicitly declared as having an integer type, and so were obvious choices for loop counters that were only temporarily required. The practice dates back further to [mathematical notation](https:\/\/en.wikipedia.org\/wiki\/Mathematical_notation \"Mathematical notation\") where [indices](https:\/\/en.wikipedia.org\/wiki\/Index_notation \"Index notation\") for [sums](https:\/\/en.wikipedia.org\/wiki\/Summation \"Summation\") and [multiplications](https:\/\/en.wikipedia.org\/wiki\/Multiplication \"Multiplication\") are often *i*, *j*, and *k*.\n\nUsing terse names for loop counters, like *i* and *j*, is discouraged by some since the purpose of the variables is not as clear as if they were given a longer more descriptive name.[\\[4\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-codecomplete-4): 383–382\n\nDifferent languages specify different rules for what value the loop counter will hold on termination of its loop, and indeed some hold that it becomes undefined. This permits a [compiler](https:\/\/en.wikipedia.org\/wiki\/Compiler \"Compiler\") to generate code that leaves any value in the loop counter, or perhaps even leaves it unchanged because the loop value was held in a register and never stored in memory. Actual behavior may even vary according to the compiler's optimization settings.\n\nModifying the loop counter within the body of the loop can lead to unexpected consequences. To prevent such problems, some languages make the loop counter [immutable](https:\/\/en.wikipedia.org\/wiki\/Immutable_object \"Immutable object\").\\[*[citation needed](https:\/\/en.wikipedia.org\/wiki\/Wikipedia:Citation_needed \"Wikipedia:Citation needed\")*\\] However, only overt changes are likely to be detected by the compiler. Situations where the address of the loop counter is passed as an argument to a [subroutine](https:\/\/en.wikipedia.org\/wiki\/Subroutine \"Subroutine\"), make it very difficult to check because the routine's behavior is in general unknowable to the compiler unless the language supports procedure signatures and argument intents.\\[*[citation needed](https:\/\/en.wikipedia.org\/wiki\/Wikipedia:Citation_needed \"Wikipedia:Citation needed\")*\\]\n\n## Early exit and continuation\n\\[[edit](https:\/\/en.wikipedia.org\/w\/index.php?title=Loop_\\(statement\\)&action=edit&section=10 \"Edit section: Early exit and continuation\")\\]\n\nSome languages may also provide supporting statements for altering how a loop's iteration proceeds. Common among these are the [*break*](https:\/\/en.wikipedia.org\/wiki\/Break_statement \"Break statement\") statement, which terminates the current loop the program is in, and the [*continue*](https:\/\/en.wikipedia.org\/wiki\/Control_flow#Continuation_with_next_iteration \"Control flow\") statement, which skips to the next iteration of the current loop.[\\[4\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-codecomplete-4): 379  These statements may have other names; For example in [Fortran 90](https:\/\/en.wikipedia.org\/wiki\/Fortran_90 \"Fortran 90\"), they are called *exit* and *cycle*.\\[*[citation needed](https:\/\/en.wikipedia.org\/wiki\/Wikipedia:Citation_needed \"Wikipedia:Citation needed\")*\\]\n\nA loop can also be terminated by [returning](https:\/\/en.wikipedia.org\/wiki\/Return_statement \"Return statement\") from the function within which it is being executed.\n\nIn the case of nested loops, the *break* and *continue* statements apply to the inner most loop. Some languages allow loops to be labelled. These statements can then be applied to any of the loops in which the program is nested.\n```\nouter_loop: (This is a label for the outermost loop)\nfor 1 ≤ i ≤ 2 do\n    for 1 ≤ j ≤ 2 do\n        display(i, j)\n        if i = 2\n            continue outer_loop\n        end if\n    repeat\nrepeat\n(This nested loop displays the pairs (1, 1), (1, 2), and (2, 1))\n```\n## Infinite loop\n\\[[edit](https:\/\/en.wikipedia.org\/w\/index.php?title=Loop_\\(statement\\)&action=edit&section=11 \"Edit section: Infinite loop\")\\]\n\nMain article: [Infinite loop](https:\/\/en.wikipedia.org\/wiki\/Infinite_loop \"Infinite loop\")\n\n|   |   |\n|---|---|\n| [![\\[icon\\]](https:\/\/upload.wikimedia.org\/wikipedia\/commons\/thumb\/1\/1c\/Wiki_letter_w_cropped.svg\/20px-Wiki_letter_w_cropped.svg.png)](https:\/\/en.wikipedia.org\/wiki\/File:Wiki_letter_w_cropped.svg) | This section **needs expansion**. You can help by [adding missing information](https:\/\/en.wikipedia.org\/w\/index.php?title=Loop_\\(statement\\)&action=edit&section=). *(January 2026)* |\n\nAn infinite loop is a loop which never terminates. This can be intentional, or the result of a [logic error](https:\/\/en.wikipedia.org\/wiki\/Logic_error \"Logic error\").\n\nSystematically detecting infinite loops is known as the [halting problem](https:\/\/en.wikipedia.org\/wiki\/Halting_problem \"Halting problem\").[\\[30\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-30)\n\nInfinite loops are useful in applications which need to perform a repeated calculation until a program terminates, such as [web servers](https:\/\/en.wikipedia.org\/wiki\/Web_servers \"Web servers\").[\\[31\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-31)\n\n## See also\n\\[[edit](https:\/\/en.wikipedia.org\/w\/index.php?title=Loop_\\(statement\\)&action=edit&section=12 \"Edit section: See also\")\\]\n\n- [Primitive recursive function](https:\/\/en.wikipedia.org\/wiki\/Primitive_recursive_function \"Primitive recursive function\")\n- [General recursive function](https:\/\/en.wikipedia.org\/wiki\/General_recursive_function \"General recursive function\")\n- [Repeat loop (disambiguation)](https:\/\/en.wikipedia.org\/wiki\/Repeat_loop_\\(disambiguation\\) \"Repeat loop (disambiguation)\")\n- [LOOP (programming language)](https:\/\/en.wikipedia.org\/wiki\/LOOP_\\(programming_language\\) \"LOOP (programming language)\") – a programming language with the property that the functions it can compute are exactly the primitive recursive functions\n\n## References\n\\[[edit](https:\/\/en.wikipedia.org\/w\/index.php?title=Loop_\\(statement\\)&action=edit&section=13 \"Edit section: References\")\\]\n\n1. **[^](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-1)**\n   Angelou, Alexandros; Dadaliaris, Antonios; Dossis, Michael; Dimitriou, Georgios (2021-11-26). [\"Branchless Code Generation for Modern Processor Architectures\"](https:\/\/doi.org\/10.1145\/3503823.3503879). *25th Pan-Hellenic Conference on Informatics*. New York, NY, USA: ACM: 300–305\\. [doi](https:\/\/en.wikipedia.org\/wiki\/Doi_\\(identifier\\) \"Doi (identifier)\"):[10\\.1145\/3503823.3503879](https:\/\/doi.org\/10.1145%2F3503823.3503879). [ISBN](https:\/\/en.wikipedia.org\/wiki\/ISBN_\\(identifier\\) \"ISBN (identifier)\")\n   \n   [978-1-4503-9555-7](https:\/\/en.wikipedia.org\/wiki\/Special:BookSources\/978-1-4503-9555-7 \"Special:BookSources\/978-1-4503-9555-7\")\n   \n   .\n2. ^ [***a***](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-joy_2-0) [***b***](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-joy_2-1)\n   Samanta, Debasis; Sarma, Monalisa (15 June 2023). [*Joy with Java: Fundamentals of Object Oriented Programming*](https:\/\/books.google.com\/books?id=34GyEAAAQBAJ). Cambridge University Press. p. 124. [ISBN](https:\/\/en.wikipedia.org\/wiki\/ISBN_\\(identifier\\) \"ISBN (identifier)\")\n   \n   [978-1-009-21190-1](https:\/\/en.wikipedia.org\/wiki\/Special:BookSources\/978-1-009-21190-1 \"Special:BookSources\/978-1-009-21190-1\")\n   \n   .\n3. ^ [***a***](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-bbc1_3-0) [***b***](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-bbc1_3-1)\n   [\"Conditional loops - Computational constructs - National 4 Computing Science Revision\"](https:\/\/web.archive.org\/web\/20211019111021\/https:\/\/www.bbc.co.uk\/bitesize\/guides\/zcg9kqt\/revision\/8). *BBC Bitesize*. Archived from [the original](https:\/\/www.bbc.co.uk\/bitesize\/guides\/zcg9kqt\/revision\/8) on 19 October 2021. Retrieved 8 January 2026.\n4. ^ [***a***](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-codecomplete_4-0) [***b***](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-codecomplete_4-1) [***c***](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-codecomplete_4-2) [***d***](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-codecomplete_4-3)\n   McConnell, Steve (9 June 2004). [*Code Complete*](https:\/\/books.google.com\/books?id=LpVCAwAAQBAJ). Pearson Education. [ISBN](https:\/\/en.wikipedia.org\/wiki\/ISBN_\\(identifier\\) \"ISBN (identifier)\")\n   \n   [978-0-7356-3697-2](https:\/\/en.wikipedia.org\/wiki\/Special:BookSources\/978-0-7356-3697-2 \"Special:BookSources\/978-0-7356-3697-2\")\n   \n   .\n5. **[^](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-5)**\n   [\"while Statement (GNU C Language Manual)\"](https:\/\/web.archive.org\/web\/20240712235744\/https:\/\/www.gnu.org\/software\/c-intro-and-ref\/manual\/html_node\/while-Statement.html). *www.gnu.org*. Archived from [the original](https:\/\/www.gnu.org\/software\/c-intro-and-ref\/manual\/html_node\/while-Statement.html) on 12 July 2024. Retrieved 8 January 2026.\n6. **[^](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-6)**\n   [\"3. An Informal Introduction to Python\"](https:\/\/web.archive.org\/web\/20251231204216\/https:\/\/docs.python.org\/3\/tutorial\/introduction.html). *Python documentation*. Archived from [the original](https:\/\/docs.python.org\/3\/tutorial\/introduction.html) on 31 December 2025. Retrieved 8 January 2026.\n7. **[^](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-7)**\n   [\"do...while - JavaScript \\| MDN\"](https:\/\/developer.mozilla.org\/en-US\/docs\/Web\/JavaScript\/Reference\/Statements\/do...while). *MDN Web Docs*. 2025-07-08. Retrieved 2026-01-22.\n8. **[^](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-8)**\n   [\"DO WHILE (FORTRAN 77 Language Reference)\"](https:\/\/web.archive.org\/web\/20230314015649\/https:\/\/docs.oracle.com\/cd\/E19957-01\/805-4939\/6j4m0vn8e\/index.html). *docs.oracle.com*. Archived from [the original](https:\/\/docs.oracle.com\/cd\/E19957-01\/805-4939\/6j4m0vn8e\/index.html) on 14 March 2023. Retrieved 8 January 2026.\n9. **[^](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-9)**\n   [\"DO command (PL\/I)\"](https:\/\/web.archive.org\/web\/20250302164825\/https:\/\/www.ibm.com\/docs\/en\/wdfrhcw\/1.4.0?topic=commands-do-command-pli). *www.ibm.com*. Archived from [the original](https:\/\/www.ibm.com\/docs\/en\/wdfrhcw\/1.4.0?topic=commands-do-command-pli) on 2 March 2025. Retrieved 22 January 2026.\n10. **[^](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-10)**\n    [\"do-while Statement (GNU C Language Manual)\"](https:\/\/web.archive.org\/web\/20240713012759\/https:\/\/www.gnu.org\/software\/c-intro-and-ref\/manual\/html_node\/do_002dwhile-Statement.html). *www.gnu.org*. Archived from [the original](https:\/\/www.gnu.org\/software\/c-intro-and-ref\/manual\/html_node\/do_002dwhile-Statement.html) on 13 July 2024. Retrieved 8 January 2026.\n11. **[^](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-11)**\n    [\"The Repeat..until statement\"](https:\/\/web.archive.org\/web\/20251109225700\/https:\/\/www.freepascal.org\/docs-html\/ref\/refsu60.html). *www.freepascal.org*. Archived from [the original](https:\/\/www.freepascal.org\/docs-html\/ref\/refsu60.html) on 9 November 2025. Retrieved 22 January 2026.\n12. **[^](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-12)**\n    [\"Programming in Lua : 4.3.3\"](https:\/\/web.archive.org\/web\/20260102100039\/https:\/\/www.lua.org\/pil\/4.3.3.html). *www.lua.org*. Archived from [the original](https:\/\/www.lua.org\/pil\/4.3.3.html) on 2 January 2026. Retrieved 22 January 2026.\n13. **[^](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-ken_13-0)**\n    [Thompson, Ken](https:\/\/en.wikipedia.org\/wiki\/Ken_Thompson \"Ken Thompson\"). [*VCF East 2019 – Brian Kernighan interviews Ken Thompson*](https:\/\/www.youtube.com\/watch?v=EY6q5dv_B-o&t=2330). *[YouTube](https:\/\/en.wikipedia.org\/wiki\/YouTube \"YouTube\")*. [Archived](https:\/\/ghostarchive.org\/varchive\/youtube\/20211212\/EY6q5dv_B-o) from the original on 2021-12-12. Retrieved 2020-11-16. \"I saw Johnson's semicolon version of the for loop and I put that in \\[B\\], I stole it.\"\n14. **[^](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-14)**\n    McConnell, Steve (9 June 2004). [*Code Complete*](https:\/\/books.google.com\/books?id=LpVCAwAAQBAJ&q=code+complete). Pearson Education. p. 367. [ISBN](https:\/\/en.wikipedia.org\/wiki\/ISBN_\\(identifier\\) \"ISBN (identifier)\")\n    \n    [978-0-7356-3697-2](https:\/\/en.wikipedia.org\/wiki\/Special:BookSources\/978-0-7356-3697-2 \"Special:BookSources\/978-0-7356-3697-2\")\n    \n    .\n15. **[^](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-15)**\n    [Wirth, Niklaus](https:\/\/en.wikipedia.org\/wiki\/Niklaus_Wirth \"Niklaus Wirth\") (1973). \"Preface\". *Systematic Programming: An Introduction*. Prentice-Hall. pp. xiii. [ISBN](https:\/\/en.wikipedia.org\/wiki\/ISBN_\\(identifier\\) \"ISBN (identifier)\")\n    \n    [0138803692](https:\/\/en.wikipedia.org\/wiki\/Special:BookSources\/0138803692 \"Special:BookSources\/0138803692\")\n    \n    .\n16. **[^](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-16)**\n    [\"DO \/ END DO\"](https:\/\/web.archive.org\/web\/20260108231419\/https:\/\/www.ibm.com\/docs\/en\/xl-fortran-linux\/16.1.0?topic=directives-do-end-do). *www.ibm.com*. 24 April 2018. Archived from [the original](https:\/\/www.ibm.com\/docs\/en\/xl-fortran-linux\/16.1.0?topic=directives-do-end-do) on 8 January 2026. Retrieved 8 January 2026.\n17. **[^](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-17)**\n    [\"PERFORM with VARYING Phrase\"](https:\/\/web.archive.org\/web\/20260108231758\/https:\/\/www.ibm.com\/docs\/en\/i\/7.5.0?topic=statement-perform-varying-phrase). *www.ibm.com*. June 2012. Archived from [the original](https:\/\/www.ibm.com\/docs\/en\/i\/7.5.0?topic=statement-perform-varying-phrase) on 8 January 2026. Retrieved 8 January 2026.\n18. **[^](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-18)**\n    [\"Zig documentation\"](https:\/\/web.archive.org\/web\/20260104121319\/https:\/\/ziglang.org\/documentation\/master\/#for). *ziglang.org*. Archived from [the original](https:\/\/ziglang.org\/documentation\/master\/#for) on 4 January 2026. 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Retrieved 2025-12-16.\n21. **[^](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-21)**\n    [\"for Statement (GNU C Language Manual)\"](https:\/\/web.archive.org\/web\/20240713014231\/https:\/\/www.gnu.org\/software\/c-intro-and-ref\/manual\/html_node\/for-Statement.html). *www.gnu.org*. Archived from [the original](https:\/\/www.gnu.org\/software\/c-intro-and-ref\/manual\/html_node\/for-Statement.html) on 13 July 2024. Retrieved 8 January 2026.\n22. **[^](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-22)**\n    [\"for statement (C++)\"](https:\/\/web.archive.org\/web\/20250928185930\/https:\/\/learn.microsoft.com\/en-us\/cpp\/cpp\/for-statement-cpp?view=msvc-170). *learn.microsoft.com*. Archived from [the original](https:\/\/learn.microsoft.com\/en-us\/cpp\/cpp\/for-statement-cpp?view=msvc-170) on 28 September 2025. Retrieved 8 January 2026.\n23. **[^](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-23)**\n    [\"The for Statement (The Java™ Tutorials \\> Learning the Java Language \\> Language Basics)\"](https:\/\/web.archive.org\/web\/20251228051928\/https:\/\/docs.oracle.com\/javase\/tutorial\/java\/nutsandbolts\/for.html). *docs.oracle.com*. Archived from [the original](https:\/\/docs.oracle.com\/javase\/tutorial\/java\/nutsandbolts\/for.html) on 28 December 2025. Retrieved 8 January 2026.\n24. **[^](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-24)**\n    [\"Iteration statements -for, foreach, do, and while - C\\# reference\"](https:\/\/web.archive.org\/web\/20251228021319\/https:\/\/learn.microsoft.com\/en-us\/dotnet\/csharp\/language-reference\/statements\/iteration-statements). *learn.microsoft.com*. Archived from [the original](https:\/\/learn.microsoft.com\/en-us\/dotnet\/csharp\/language-reference\/statements\/iteration-statements) on 28 December 2025. Retrieved 8 January 2026.\n25. **[^](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-25)**\n    [\"Perl for Loop\"](https:\/\/web.archive.org\/web\/20250607160051\/https:\/\/www.perltutorial.org\/perl-for-loop\/). *Perl Tutorial*. Archived from [the original](https:\/\/www.perltutorial.org\/perl-for-loop\/) on 7 June 2025. Retrieved 8 January 2026.\n26. **[^](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-26)**\n    [\"FORALL\"](https:\/\/web.archive.org\/web\/20260101223642\/https:\/\/www.intel.com\/content\/www\/us\/en\/docs\/fortran-compiler\/developer-guide-reference\/2025-2\/forall.html). *Intel*. Archived from [the original](https:\/\/www.intel.com\/content\/www\/us\/en\/docs\/fortran-compiler\/developer-guide-reference\/2025-2\/forall.html) on 1 January 2026. Retrieved 8 January 2026.\n27. **[^](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-27)**\n    Hinsen, Konrad (2009). [\"The Promises of Functional Programming\"](https:\/\/doi.org\/10.1109\/mcse.2009.129). *Computing in Science & Engineering*. **11** (4): 86–90\\. [Bibcode](https:\/\/en.wikipedia.org\/wiki\/Bibcode_\\(identifier\\) \"Bibcode (identifier)\"):[2009CSE....11d..86H](https:\/\/ui.adsabs.harvard.edu\/abs\/2009CSE....11d..86H). [doi](https:\/\/en.wikipedia.org\/wiki\/Doi_\\(identifier\\) \"Doi (identifier)\"):[10\\.1109\/mcse.2009.129](https:\/\/doi.org\/10.1109%2Fmcse.2009.129). [ISSN](https:\/\/en.wikipedia.org\/wiki\/ISSN_\\(identifier\\) \"ISSN (identifier)\") [1521-9615](https:\/\/search.worldcat.org\/issn\/1521-9615).\n28. **[^](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-28)**\n    Clinger, William D. (1998). \"Proper tail recursion and space efficiency\". *Proceedings of the ACM SIGPLAN 1998 conference on Programming language design and implementation*. New York, NY, USA: ACM. pp. 174–185\\. [doi](https:\/\/en.wikipedia.org\/wiki\/Doi_\\(identifier\\) \"Doi (identifier)\"):[10\\.1145\/277650.277719](https:\/\/doi.org\/10.1145%2F277650.277719). [ISBN](https:\/\/en.wikipedia.org\/wiki\/ISBN_\\(identifier\\) \"ISBN (identifier)\")\n    \n    [0-89791-987-4](https:\/\/en.wikipedia.org\/wiki\/Special:BookSources\/0-89791-987-4 \"Special:BookSources\/0-89791-987-4\")\n    \n    .\n29. **[^](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-29)** <http:\/\/www.knosof.co.uk\/vulnerabilities\/loopcntrl.pdf> Analysis of loop control variables in C\n30. **[^](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-30)**\n    Lee, Sarah. [\"Turing's Halting Problem Explained\"](https:\/\/www.numberanalytics.com\/blog\/ultimate-guide-turing-halting-problem). *www.numberanalytics.com*. Retrieved 2026-01-22.\n31. **[^](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-31)**\n    [\"What is an infinite loop (endless loop)?\"](https:\/\/www.techtarget.com\/whatis\/definition\/infinite-loop-endless-loop). *WhatIs*. Retrieved 2026-01-22.\n\n![](https:\/\/en.wikipedia.org\/wiki\/Special:CentralAutoLogin\/start?useformat=desktop&type=1x1&usesul3=1)\n\nRetrieved from \"<https:\/\/en.wikipedia.org\/w\/index.php?title=Loop_(statement)&oldid=1343948330#Pre-test_loop>\"\n\n[Category](https:\/\/en.wikipedia.org\/wiki\/Help:Category \"Help:Category\"):\n\n- [Control flow](https:\/\/en.wikipedia.org\/wiki\/Category:Control_flow \"Category:Control flow\")\n\nHidden categories:\n\n- [Articles with short description](https:\/\/en.wikipedia.org\/wiki\/Category:Articles_with_short_description \"Category:Articles with short description\")\n- [Short description is different from Wikidata](https:\/\/en.wikipedia.org\/wiki\/Category:Short_description_is_different_from_Wikidata \"Category:Short description is different from Wikidata\")\n- [Articles needing additional references from January 2026](https:\/\/en.wikipedia.org\/wiki\/Category:Articles_needing_additional_references_from_January_2026 \"Category:Articles needing additional references from January 2026\")\n- [All articles needing additional references](https:\/\/en.wikipedia.org\/wiki\/Category:All_articles_needing_additional_references \"Category:All articles needing additional references\")\n- [All articles with unsourced statements](https:\/\/en.wikipedia.org\/wiki\/Category:All_articles_with_unsourced_statements \"Category:All articles with unsourced statements\")\n- [Articles with unsourced statements from December 2025](https:\/\/en.wikipedia.org\/wiki\/Category:Articles_with_unsourced_statements_from_December_2025 \"Category:Articles with unsourced statements from December 2025\")\n- [Articles with unsourced statements from January 2026](https:\/\/en.wikipedia.org\/wiki\/Category:Articles_with_unsourced_statements_from_January_2026 \"Category:Articles with unsourced statements from January 2026\")\n- [Articles to be expanded from January 2026](https:\/\/en.wikipedia.org\/wiki\/Category:Articles_to_be_expanded_from_January_2026 \"Category:Articles to be expanded from January 2026\")\n- [All articles to be expanded](https:\/\/en.wikipedia.org\/wiki\/Category:All_articles_to_be_expanded \"Category:All articles to be expanded\")\n- [Articles with unsourced statements from August 2009](https:\/\/en.wikipedia.org\/wiki\/Category:Articles_with_unsourced_statements_from_August_2009 \"Category:Articles with unsourced statements from August 2009\")\n\n- This page was last edited on 17 March 2026, at 10:34 (UTC).\n- Text is available under the [Creative Commons Attribution-ShareAlike 4.0 License](https:\/\/en.wikipedia.org\/wiki\/Wikipedia:Text_of_the_Creative_Commons_Attribution-ShareAlike_4.0_International_License \"Wikipedia:Text of the Creative Commons Attribution-ShareAlike 4.0 International License\"); additional terms may apply. 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Wikipedia® is a registered trademark of the [Wikimedia Foundation, Inc.](https:\/\/wikimediafoundation.org\/), a non-profit organization.\n\n- [Privacy policy](https:\/\/foundation.wikimedia.org\/wiki\/Special:MyLanguage\/Policy:Privacy_policy)\n- [About Wikipedia](https:\/\/en.wikipedia.org\/wiki\/Wikipedia:About)\n- [Disclaimers](https:\/\/en.wikipedia.org\/wiki\/Wikipedia:General_disclaimer)\n- [Contact Wikipedia](https:\/\/en.wikipedia.org\/wiki\/Wikipedia:Contact_us)\n- [Legal & safety contacts](https:\/\/foundation.wikimedia.org\/wiki\/Special:MyLanguage\/Legal:Wikimedia_Foundation_Legal_and_Safety_Contact_Information)\n- [Code of Conduct](https:\/\/foundation.wikimedia.org\/wiki\/Special:MyLanguage\/Policy:Universal_Code_of_Conduct)\n- [Developers](https:\/\/developer.wikimedia.org\/)\n- [Statistics](https:\/\/stats.wikimedia.org\/#\/en.wikipedia.org)\n- [Cookie statement](https:\/\/foundation.wikimedia.org\/wiki\/Special:MyLanguage\/Policy:Cookie_statement)\n- [Mobile view](https:\/\/en.wikipedia.org\/w\/index.php?title=Loop_\\(statement\\)&mobileaction=toggle_view_mobile#Pre-test_loop)\n\n- [![Wikimedia Foundation](https:\/\/en.wikipedia.org\/static\/images\/footer\/wikimedia.svg)](https:\/\/www.wikimedia.org\/)\n- [![Powered by MediaWiki](https:\/\/en.wikipedia.org\/w\/resources\/assets\/mediawiki_compact.svg)](https:\/\/www.mediawiki.org\/)\n\nSearch\n\nToggle the table of contents\n\nLoop (statement)\n\n25 languages\n\n[Add topic](https:\/\/en.wikipedia.org\/wiki\/While_loop)","attrs_readable_markdown":"From Wikipedia, the free encyclopedia\n\nIn [computer programming](https:\/\/en.wikipedia.org\/wiki\/Computer_programming \"Computer programming\"), a **loop** is a [control flow](https:\/\/en.wikipedia.org\/wiki\/Control_flow \"Control flow\") [statement](https:\/\/en.wikipedia.org\/wiki\/Statement_\\(computer_science\\) \"Statement (computer science)\") that allows code to be executed repeatedly, usually with minor alterations between repetitions. Loops can be used to perform a repeated action on all items in a [collection](https:\/\/en.wikipedia.org\/wiki\/Collection_\\(abstract_data_type\\) \"Collection (abstract data type)\"), or to implement a long lived program.\n\nLoops are a feature of [high-level programming languages](https:\/\/en.wikipedia.org\/wiki\/High-level_programming_languages \"High-level programming languages\"). In [low-level programming languages](https:\/\/en.wikipedia.org\/wiki\/Low-level_programming_languages \"Low-level programming languages\") the same functionality is achieved using [jumps](https:\/\/en.wikipedia.org\/wiki\/Control_flow#Jump \"Control flow\"). When a program is [compiled](https:\/\/en.wikipedia.org\/wiki\/Compiler \"Compiler\") to [machine code](https:\/\/en.wikipedia.org\/wiki\/Machine_code \"Machine code\"), looping may be achieved using jumps; but some loops can be [optimized](https:\/\/en.wikipedia.org\/wiki\/Code_optimization \"Code optimization\") to run without jumping.[\\[1\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-1)\n\nUsually, loops are expected to run for a finite number of iteration.\\[*[citation needed](https:\/\/en.wikipedia.org\/wiki\/Wikipedia:Citation_needed \"Wikipedia:Citation needed\")*\\] Without proper care, loops may accidentally be created that have no possibility of terminating. Such loops are called [infinite loops](https:\/\/en.wikipedia.org\/wiki\/Infinite_loop \"Infinite loop\"). The problem of determining whether a program contains an infinite loop is known as the [halting problem](https:\/\/en.wikipedia.org\/wiki\/Halting_problem \"Halting problem\").\n\nA **conditional loop** (also known as an **indeterminate loop**[\\[2\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-joy-2)) is a loop that determines whether to terminate based on a logical condition.[\\[3\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-bbc1-3) These loops are flexible, but there exact behavior can be difficult to reason about.[\\[4\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-codecomplete-4): 368\n\nA conditional loop is usually composed of two parts: a *condition* and a *body*. The *condition* is a logical statement depending on the state of the program and the *body* is a block of code that runs as long as the *condition* holds.[\\[3\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-bbc1-3)\n\nA common misconception is that the execution of the *body* terminates as soon as the *condition* does not hold anymore; but this is usually not the case.[\\[4\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-codecomplete-4): 368  In most programming languages, the *condition* is checked once for every execution of the *body*. When the *condition* is checked is not standardized and some programming languages contain multiple conditional looping structures with different rules about when the *condition* is assessed.\\[*[citation needed](https:\/\/en.wikipedia.org\/wiki\/Wikipedia:Citation_needed \"Wikipedia:Citation needed\")*\\]\n\nA **pre-test loop** is a conditional loop where the *condition* is checked before the *body* is executed. More precisely, the *condition* is checked and if it holds the *body* is execute. Afterwards, the *condition* is checked again, and if it holds the *body* is executed again. This process repeats until the *condition* does not hold. Many programming languages call this loop a *while loop* and refer to it with the [keyword](https:\/\/en.wikipedia.org\/wiki\/Reserved_word \"Reserved word\") *while*. They are commonly formatted in manner similar to\n```\nwhile condition do\n    body\nrepeat\n```\nInstead of the keywords *do* and *repeat* others methods are sometime use to indicate where the *body* begins and ends, such as [curly braces](https:\/\/en.wikipedia.org\/wiki\/Curly_braces \"Curly braces\")[\\[5\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-5) or [whitespace](https:\/\/en.wikipedia.org\/wiki\/Whitespace_characters \"Whitespace characters\").[\\[6\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-6)\n\nFor example, the following code fragment first checks whether *x* is less than five, which it is, so the *body* is entered. There, *x* is displayed and then incremented by one. After executing the statements in the *body*, the *condition* is checked again, and the loop is executed again. This process repeats until *x* has the value five.\n```\nx ← 0\nwhile x < 5 do\n    display(x)\n    x ← x + 1\nrepeat\n```\n[![](https:\/\/upload.wikimedia.org\/wikipedia\/commons\/thumb\/9\/92\/Do-while-loop-diagram.svg\/250px-Do-while-loop-diagram.svg.png)](https:\/\/en.wikipedia.org\/wiki\/File:Do-while-loop-diagram.svg)\n\nDo-While loop flow diagram\n\nA **post-test loop** is a conditional loop where the *condition* is checked after the *body* is executed. More precisely, the *body* is executed and afterwards the *condition* is checked. If it holds the *body* is run again and then the *condition* is checked. This is repeated until the *condition* does not hold. This is sometimes called a *do-while loop* due to the syntax used in various programming languages,[\\[7\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-7) although this can be confusing since [Fortran](https:\/\/en.wikipedia.org\/wiki\/Fortran \"Fortran\") and [PL\/I](https:\/\/en.wikipedia.org\/wiki\/PL\/I \"PL\/I\") use the syntax \"DO WHILE\" for pre-test loops.[\\[8\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-8)[\\[9\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-9) Post-test loops are commonly formatted in manner similar to\n```\ndo\n    body\nrepeat while condition\n```\nInstead of the keywords *do* and *repeat* others methods are sometime use to indicate where the *body* begins and ends, such as curly braces.[\\[10\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-10)\n\nSome [languages](https:\/\/en.wikipedia.org\/wiki\/Programming_language \"Programming language\") may use a different naming convention for this type of loop. For example, the [Pascal](https:\/\/en.wikipedia.org\/wiki\/Pascal_programming_language \"Pascal programming language\") and [Lua](https:\/\/en.wikipedia.org\/wiki\/Lua_\\(programming_language\\) \"Lua (programming language)\") languages have a \"*repeat until*\" loop, which continues to run *until* the control expression is true and then terminates.[\\[11\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-11)[\\[12\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-12)\n\n### Three-part for loop\n\\[[edit](https:\/\/en.wikipedia.org\/w\/index.php?title=Loop_\\(statement\\)&action=edit&section=5 \"Edit section: Three-part for loop\")\\]\n\n[![](https:\/\/upload.wikimedia.org\/wikipedia\/commons\/thumb\/d\/d1\/For_loop_example.svg\/250px-For_loop_example.svg.png)](https:\/\/en.wikipedia.org\/wiki\/File:For_loop_example.svg)\n\nFlow diagram of a for loop that prints five asterisks.\n\nA **three-part for loop**, popularized by C, has two additional parts: [*initialization*](https:\/\/en.wikipedia.org\/wiki\/Declaration_\\(computer_programming\\) \"Declaration (computer programming)\") ([loop variant](https:\/\/en.wikipedia.org\/wiki\/Loop_variant \"Loop variant\")), and *increment*, both of which are blocks of code. The *initialization* is intended as code that prepares the loop and is run once in the beginning and *increment* is used to update the state of the program after each iteration of the loop. Otherwise, the three-part for loop is a pre-test loop. They are commonly formatted in manner similar to\n```\nfor initialization, condition, increment do\n    body\nrepeat\n```\nThis syntax came from [B](https:\/\/en.wikipedia.org\/wiki\/B_\\(programming_language\\) \"B (programming language)\") and was originally invented by [Stephen C. Johnson](https:\/\/en.wikipedia.org\/wiki\/Stephen_C._Johnson \"Stephen C. Johnson\").[\\[13\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-ken-13) The following C code is an example of a three part loop that prints the numbers from 0 to 4.\n```\nfor (int i = 0; i < 5; i++) {\n    printf(\"%d\\n\", i);\n}\n```\n### Equivalent constructs\n\\[[edit](https:\/\/en.wikipedia.org\/w\/index.php?title=Loop_\\(statement\\)&action=edit&section=6 \"Edit section: Equivalent constructs\")\\]\n\nAssuming there is a function called *do\\_work()* that does some work, the following are equivalent.\\[*[citation needed](https:\/\/en.wikipedia.org\/wiki\/Wikipedia:Citation_needed \"Wikipedia:Citation needed\")*\\]\n\nAs long as the *continue* statement is not used, the above is technically equivalent to the following (though these examples are not typical or modern style used in everyday computers):\n```\nwhile true do\n    do_work()\n    if condition is not true then\n        break\n    end if\nrepeat\n```\nor\n```\nLOOPSTART:\ndo_work()\nif condition then\n    goto LOOPSTART\nend if\n```\n[![](https:\/\/upload.wikimedia.org\/wikipedia\/commons\/thumb\/1\/13\/For-Loop-Mint-Programming-Language-Type-2.gif\/250px-For-Loop-Mint-Programming-Language-Type-2.gif)](https:\/\/en.wikipedia.org\/wiki\/File:For-Loop-Mint-Programming-Language-Type-2.gif)\n\nforeach loops are almost always used to iterate over items in a sequence of elements.\n\nAn **enumeration** (also known as an **determinate loop**[\\[2\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-joy-2)) is a loop intended to iterate over all the items of a collection.[\\[14\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-14) It is not as flexible as a conditional loop; but it is more predictable.\\[*[citation needed](https:\/\/en.wikipedia.org\/wiki\/Wikipedia:Citation_needed \"Wikipedia:Citation needed\")*\\] For example, it is easier to guarantee that enumerations [terminate](https:\/\/en.wikipedia.org\/wiki\/Terminate \"Terminate\") and they avoid potential [off-by-one errors](https:\/\/en.wikipedia.org\/wiki\/Off-by-one_error \"Off-by-one error\").\\[*[citation needed](https:\/\/en.wikipedia.org\/wiki\/Wikipedia:Citation_needed \"Wikipedia:Citation needed\")*\\] Enumerations can be implemented using an [iterator](https:\/\/en.wikipedia.org\/wiki\/Iterator \"Iterator\"), whether implicitly or explicitly. They are commonly formatted in manner similar to\n```\nfor item in collection\n    body\nrepeat\n```\nDepending on the programming language, various keywords are used to invoke enumerations. For example, descendants of [ALGOL](https:\/\/en.wikipedia.org\/wiki\/ALGOL \"ALGOL\") use `for`,[\\[15\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-15) while descendants of [Fortran](https:\/\/en.wikipedia.org\/wiki\/Fortran \"Fortran\") use `do`[\\[16\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-16) and [COBOL](https:\/\/en.wikipedia.org\/wiki\/COBOL \"COBOL\") uses `PERFORM VARYING`.[\\[17\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-17)\n\nEnumerations are sometimes called \"for loops,\" for example in [Zig](https:\/\/en.wikipedia.org\/wiki\/Zig_\\(programming_language\\) \"Zig (programming language)\") and [Rust](https:\/\/en.wikipedia.org\/wiki\/Rust_\\(programming_language\\) \"Rust (programming language)\").[\\[18\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-18)[\\[19\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-19) This can be confusing since many of the most popular[\\[20\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-20) programming languages, such as C, [C++](https:\/\/en.wikipedia.org\/wiki\/C%2B%2B \"C++\"), and [Java](https:\/\/en.wikipedia.org\/wiki\/Java_\\(programming_language\\) \"Java (programming language)\"), use that term for the three-part for loop,[\\[21\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-21)[\\[22\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-22)[\\[23\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-23) which is not an enumeration. Other programming languages, such as [Perl](https:\/\/en.wikipedia.org\/wiki\/Perl \"Perl\") and [C\\#](https:\/\/en.wikipedia.org\/wiki\/C \"C\"), avoid this confusion by using the term \"foreach loop.\"[\\[24\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-24)[\\[25\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-25)\n\nThe order in which the items in the collection are iterated through depends on the programming language. [Fortran 95](https:\/\/en.wikipedia.org\/wiki\/Fortran_95 \"Fortran 95\") has a loop, invoked using the keyword `FORALL`, that is independent of this order. It has the effect of executing each iteration of the loop at the same time. This feature was made obsolescent in [Fortran 2018](https:\/\/en.wikipedia.org\/wiki\/Fortran_2018 \"Fortran 2018\").[\\[26\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-26)\n\n## Loops in functional programming\n\\[[edit](https:\/\/en.wikipedia.org\/w\/index.php?title=Loop_\\(statement\\)&action=edit&section=8 \"Edit section: Loops in functional programming\")\\]\n\nIn most [functional programming languages](https:\/\/en.wikipedia.org\/wiki\/Functional_programming \"Functional programming\"), [recursion](https:\/\/en.wikipedia.org\/wiki\/Recursion_\\(computer_science\\) \"Recursion (computer science)\") is used instead of traditional loops. This is due to the fact that variables are [immutable](https:\/\/en.wikipedia.org\/wiki\/Immutable_object \"Immutable object\"), and therefore the *increment* step of a loop cannot occur.[\\[27\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-27)\n\nTo avoid running into [stack overflow](https:\/\/en.wikipedia.org\/wiki\/Stack_overflow \"Stack overflow\") errors for long loops, functional programming languages implement [tail call optimisation](https:\/\/en.wikipedia.org\/wiki\/Tail_call \"Tail call\"), which allows the same [stack frame](https:\/\/en.wikipedia.org\/wiki\/Call_stack \"Call stack\") to be used for each iteration of the loop, compiling to effectively the same code as a *while* or *for* loop.[\\[28\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-28)\n\nSome languages, such as [Haskell](https:\/\/en.wikipedia.org\/wiki\/Haskell \"Haskell\"), have a special syntax known as a [list comprehension](https:\/\/en.wikipedia.org\/wiki\/List_comprehension \"List comprehension\"), which is similar to enumeration, iterating over the contents of a list and transforming it into a new list.\n\nA  **loop counter** is a control variable that controls the iterations of a loop. Loop counters change with each iteration of a loop, providing a unique value for each iteration. The loop counter is used to decide when the loop should terminate. It is so named because most uses of this construct result in the variable taking on a range of integer values.\n\nA common [identifier naming convention](https:\/\/en.wikipedia.org\/wiki\/Identifier_naming_convention \"Identifier naming convention\") is for the loop counter to use the variable names *i*, *j*, and *k* (and so on if needed),[\\[29\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-29) where *i* would be the most outer loop, *j* the next inner loop, etc. This style is generally agreed to have originated from the early programming of Fortran\\[*[citation needed](https:\/\/en.wikipedia.org\/wiki\/Wikipedia:Citation_needed \"Wikipedia:Citation needed\")*\\], where these variable names beginning with these letters were implicitly declared as having an integer type, and so were obvious choices for loop counters that were only temporarily required. The practice dates back further to [mathematical notation](https:\/\/en.wikipedia.org\/wiki\/Mathematical_notation \"Mathematical notation\") where [indices](https:\/\/en.wikipedia.org\/wiki\/Index_notation \"Index notation\") for [sums](https:\/\/en.wikipedia.org\/wiki\/Summation \"Summation\") and [multiplications](https:\/\/en.wikipedia.org\/wiki\/Multiplication \"Multiplication\") are often *i*, *j*, and *k*.\n\nUsing terse names for loop counters, like *i* and *j*, is discouraged by some since the purpose of the variables is not as clear as if they were given a longer more descriptive name.[\\[4\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-codecomplete-4): 383–382\n\nDifferent languages specify different rules for what value the loop counter will hold on termination of its loop, and indeed some hold that it becomes undefined. This permits a [compiler](https:\/\/en.wikipedia.org\/wiki\/Compiler \"Compiler\") to generate code that leaves any value in the loop counter, or perhaps even leaves it unchanged because the loop value was held in a register and never stored in memory. Actual behavior may even vary according to the compiler's optimization settings.\n\nModifying the loop counter within the body of the loop can lead to unexpected consequences. To prevent such problems, some languages make the loop counter [immutable](https:\/\/en.wikipedia.org\/wiki\/Immutable_object \"Immutable object\").\\[*[citation needed](https:\/\/en.wikipedia.org\/wiki\/Wikipedia:Citation_needed \"Wikipedia:Citation needed\")*\\] However, only overt changes are likely to be detected by the compiler. Situations where the address of the loop counter is passed as an argument to a [subroutine](https:\/\/en.wikipedia.org\/wiki\/Subroutine \"Subroutine\"), make it very difficult to check because the routine's behavior is in general unknowable to the compiler unless the language supports procedure signatures and argument intents.\\[*[citation needed](https:\/\/en.wikipedia.org\/wiki\/Wikipedia:Citation_needed \"Wikipedia:Citation needed\")*\\]\n\n## Early exit and continuation\n\\[[edit](https:\/\/en.wikipedia.org\/w\/index.php?title=Loop_\\(statement\\)&action=edit&section=10 \"Edit section: Early exit and continuation\")\\]\n\nSome languages may also provide supporting statements for altering how a loop's iteration proceeds. Common among these are the [*break*](https:\/\/en.wikipedia.org\/wiki\/Break_statement \"Break statement\") statement, which terminates the current loop the program is in, and the [*continue*](https:\/\/en.wikipedia.org\/wiki\/Control_flow#Continuation_with_next_iteration \"Control flow\") statement, which skips to the next iteration of the current loop.[\\[4\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-codecomplete-4): 379  These statements may have other names; For example in [Fortran 90](https:\/\/en.wikipedia.org\/wiki\/Fortran_90 \"Fortran 90\"), they are called *exit* and *cycle*.\\[*[citation needed](https:\/\/en.wikipedia.org\/wiki\/Wikipedia:Citation_needed \"Wikipedia:Citation needed\")*\\]\n\nA loop can also be terminated by [returning](https:\/\/en.wikipedia.org\/wiki\/Return_statement \"Return statement\") from the function within which it is being executed.\n\nIn the case of nested loops, the *break* and *continue* statements apply to the inner most loop. Some languages allow loops to be labelled. These statements can then be applied to any of the loops in which the program is nested.\n```\nouter_loop: (This is a label for the outermost loop)\nfor 1 ≤ i ≤ 2 do\n    for 1 ≤ j ≤ 2 do\n        display(i, j)\n        if i = 2\n            continue outer_loop\n        end if\n    repeat\nrepeat\n(This nested loop displays the pairs (1, 1), (1, 2), and (2, 1))\n```\nAn infinite loop is a loop which never terminates. This can be intentional, or the result of a [logic error](https:\/\/en.wikipedia.org\/wiki\/Logic_error \"Logic error\").\n\nSystematically detecting infinite loops is known as the [halting problem](https:\/\/en.wikipedia.org\/wiki\/Halting_problem \"Halting problem\").[\\[30\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-30)\n\nInfinite loops are useful in applications which need to perform a repeated calculation until a program terminates, such as [web servers](https:\/\/en.wikipedia.org\/wiki\/Web_servers \"Web servers\").[\\[31\\]](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_note-31)\n\n- [Primitive recursive function](https:\/\/en.wikipedia.org\/wiki\/Primitive_recursive_function \"Primitive recursive function\")\n- [General recursive function](https:\/\/en.wikipedia.org\/wiki\/General_recursive_function \"General recursive function\")\n- [Repeat loop (disambiguation)](https:\/\/en.wikipedia.org\/wiki\/Repeat_loop_\\(disambiguation\\) \"Repeat loop (disambiguation)\")\n- [LOOP (programming language)](https:\/\/en.wikipedia.org\/wiki\/LOOP_\\(programming_language\\) \"LOOP (programming language)\") – a programming language with the property that the functions it can compute are exactly the primitive recursive functions\n\n1. **[^](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-1)**\n   Angelou, Alexandros; Dadaliaris, Antonios; Dossis, Michael; Dimitriou, Georgios (2021-11-26). [\"Branchless Code Generation for Modern Processor Architectures\"](https:\/\/doi.org\/10.1145\/3503823.3503879). *25th Pan-Hellenic Conference on Informatics*. New York, NY, USA: ACM: 300–305\\. [doi](https:\/\/en.wikipedia.org\/wiki\/Doi_\\(identifier\\) \"Doi (identifier)\"):[10\\.1145\/3503823.3503879](https:\/\/doi.org\/10.1145%2F3503823.3503879). [ISBN](https:\/\/en.wikipedia.org\/wiki\/ISBN_\\(identifier\\) \"ISBN (identifier)\")\n   \n   [978-1-4503-9555-7](https:\/\/en.wikipedia.org\/wiki\/Special:BookSources\/978-1-4503-9555-7 \"Special:BookSources\/978-1-4503-9555-7\")\n   \n   .\n2. ^ [***a***](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-joy_2-0) [***b***](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-joy_2-1)\n   Samanta, Debasis; Sarma, Monalisa (15 June 2023). [*Joy with Java: Fundamentals of Object Oriented Programming*](https:\/\/books.google.com\/books?id=34GyEAAAQBAJ). Cambridge University Press. p. 124. [ISBN](https:\/\/en.wikipedia.org\/wiki\/ISBN_\\(identifier\\) \"ISBN (identifier)\")\n   \n   [978-1-009-21190-1](https:\/\/en.wikipedia.org\/wiki\/Special:BookSources\/978-1-009-21190-1 \"Special:BookSources\/978-1-009-21190-1\")\n   \n   .\n3. ^ [***a***](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-bbc1_3-0) [***b***](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-bbc1_3-1)\n   [\"Conditional loops - Computational constructs - National 4 Computing Science Revision\"](https:\/\/web.archive.org\/web\/20211019111021\/https:\/\/www.bbc.co.uk\/bitesize\/guides\/zcg9kqt\/revision\/8). *BBC Bitesize*. Archived from [the original](https:\/\/www.bbc.co.uk\/bitesize\/guides\/zcg9kqt\/revision\/8) on 19 October 2021. Retrieved 8 January 2026.\n4. ^ [***a***](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-codecomplete_4-0) [***b***](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-codecomplete_4-1) [***c***](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-codecomplete_4-2) [***d***](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-codecomplete_4-3)\n   McConnell, Steve (9 June 2004). [*Code Complete*](https:\/\/books.google.com\/books?id=LpVCAwAAQBAJ). Pearson Education. 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[*VCF East 2019 – Brian Kernighan interviews Ken Thompson*](https:\/\/www.youtube.com\/watch?v=EY6q5dv_B-o&t=2330). *[YouTube](https:\/\/en.wikipedia.org\/wiki\/YouTube \"YouTube\")*. [Archived](https:\/\/ghostarchive.org\/varchive\/youtube\/20211212\/EY6q5dv_B-o) from the original on 2021-12-12. Retrieved 2020-11-16. \"I saw Johnson's semicolon version of the for loop and I put that in \\[B\\], I stole it.\"\n14. **[^](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-14)**\n    McConnell, Steve (9 June 2004). [*Code Complete*](https:\/\/books.google.com\/books?id=LpVCAwAAQBAJ&q=code+complete). Pearson Education. p. 367. 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Archived from [the original](https:\/\/www.ibm.com\/docs\/en\/xl-fortran-linux\/16.1.0?topic=directives-do-end-do) on 8 January 2026. Retrieved 8 January 2026.\n17. **[^](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-17)**\n    [\"PERFORM with VARYING Phrase\"](https:\/\/web.archive.org\/web\/20260108231758\/https:\/\/www.ibm.com\/docs\/en\/i\/7.5.0?topic=statement-perform-varying-phrase). *www.ibm.com*. June 2012. Archived from [the original](https:\/\/www.ibm.com\/docs\/en\/i\/7.5.0?topic=statement-perform-varying-phrase) on 8 January 2026. Retrieved 8 January 2026.\n18. **[^](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-18)**\n    [\"Zig documentation\"](https:\/\/web.archive.org\/web\/20260104121319\/https:\/\/ziglang.org\/documentation\/master\/#for). *ziglang.org*. Archived from [the original](https:\/\/ziglang.org\/documentation\/master\/#for) on 4 January 2026. Retrieved 8 January 2026.\n19. **[^](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-19)**\n    [\"Looping Through a Collection with for\"](https:\/\/web.archive.org\/web\/20251219092527\/https:\/\/doc.rust-lang.org\/stable\/book\/ch03-05-control-flow.html#looping-through-a-collection-with-for). *rust-lang.org*. Archived from [the original](https:\/\/doc.rust-lang.org\/stable\/book\/ch03-05-control-flow.html#looping-through-a-collection-with-for) on 19 December 2025. Retrieved 8 January 2026.\n20. **[^](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-20)**\n    [\"TIOBE Index for September 2024\"](https:\/\/web.archive.org\/web\/20260104151245\/https:\/\/www.tiobe.com\/tiobe-index\/). Archived from [the original](https:\/\/www.tiobe.com\/tiobe-index\/) on January 4, 2026. Retrieved 2025-12-16.\n21. **[^](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-21)**\n    [\"for Statement (GNU C Language Manual)\"](https:\/\/web.archive.org\/web\/20240713014231\/https:\/\/www.gnu.org\/software\/c-intro-and-ref\/manual\/html_node\/for-Statement.html). *www.gnu.org*. Archived from [the original](https:\/\/www.gnu.org\/software\/c-intro-and-ref\/manual\/html_node\/for-Statement.html) on 13 July 2024. Retrieved 8 January 2026.\n22. **[^](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-22)**\n    [\"for statement (C++)\"](https:\/\/web.archive.org\/web\/20250928185930\/https:\/\/learn.microsoft.com\/en-us\/cpp\/cpp\/for-statement-cpp?view=msvc-170). *learn.microsoft.com*. Archived from [the original](https:\/\/learn.microsoft.com\/en-us\/cpp\/cpp\/for-statement-cpp?view=msvc-170) on 28 September 2025. Retrieved 8 January 2026.\n23. **[^](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-23)**\n    [\"The for Statement (The Java™ Tutorials \\> Learning the Java Language \\> Language Basics)\"](https:\/\/web.archive.org\/web\/20251228051928\/https:\/\/docs.oracle.com\/javase\/tutorial\/java\/nutsandbolts\/for.html). *docs.oracle.com*. Archived from [the original](https:\/\/docs.oracle.com\/javase\/tutorial\/java\/nutsandbolts\/for.html) on 28 December 2025. Retrieved 8 January 2026.\n24. **[^](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-24)**\n    [\"Iteration statements -for, foreach, do, and while - C\\# reference\"](https:\/\/web.archive.org\/web\/20251228021319\/https:\/\/learn.microsoft.com\/en-us\/dotnet\/csharp\/language-reference\/statements\/iteration-statements). *learn.microsoft.com*. Archived from [the original](https:\/\/learn.microsoft.com\/en-us\/dotnet\/csharp\/language-reference\/statements\/iteration-statements) on 28 December 2025. Retrieved 8 January 2026.\n25. **[^](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-25)**\n    [\"Perl for Loop\"](https:\/\/web.archive.org\/web\/20250607160051\/https:\/\/www.perltutorial.org\/perl-for-loop\/). *Perl Tutorial*. Archived from [the original](https:\/\/www.perltutorial.org\/perl-for-loop\/) on 7 June 2025. Retrieved 8 January 2026.\n26. **[^](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-26)**\n    [\"FORALL\"](https:\/\/web.archive.org\/web\/20260101223642\/https:\/\/www.intel.com\/content\/www\/us\/en\/docs\/fortran-compiler\/developer-guide-reference\/2025-2\/forall.html). *Intel*. Archived from [the original](https:\/\/www.intel.com\/content\/www\/us\/en\/docs\/fortran-compiler\/developer-guide-reference\/2025-2\/forall.html) on 1 January 2026. Retrieved 8 January 2026.\n27. **[^](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-27)**\n    Hinsen, Konrad (2009). [\"The Promises of Functional Programming\"](https:\/\/doi.org\/10.1109\/mcse.2009.129). *Computing in Science & Engineering*. **11** (4): 86–90\\. [Bibcode](https:\/\/en.wikipedia.org\/wiki\/Bibcode_\\(identifier\\) \"Bibcode (identifier)\"):[2009CSE....11d..86H](https:\/\/ui.adsabs.harvard.edu\/abs\/2009CSE....11d..86H). [doi](https:\/\/en.wikipedia.org\/wiki\/Doi_\\(identifier\\) \"Doi (identifier)\"):[10\\.1109\/mcse.2009.129](https:\/\/doi.org\/10.1109%2Fmcse.2009.129). [ISSN](https:\/\/en.wikipedia.org\/wiki\/ISSN_\\(identifier\\) \"ISSN (identifier)\") [1521-9615](https:\/\/search.worldcat.org\/issn\/1521-9615).\n28. **[^](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-28)**\n    Clinger, William D. (1998). \"Proper tail recursion and space efficiency\". *Proceedings of the ACM SIGPLAN 1998 conference on Programming language design and implementation*. New York, NY, USA: ACM. pp. 174–185\\. [doi](https:\/\/en.wikipedia.org\/wiki\/Doi_\\(identifier\\) \"Doi (identifier)\"):[10\\.1145\/277650.277719](https:\/\/doi.org\/10.1145%2F277650.277719). [ISBN](https:\/\/en.wikipedia.org\/wiki\/ISBN_\\(identifier\\) \"ISBN (identifier)\")\n    \n    [0-89791-987-4](https:\/\/en.wikipedia.org\/wiki\/Special:BookSources\/0-89791-987-4 \"Special:BookSources\/0-89791-987-4\")\n    \n    .\n29. **[^](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-29)** <http:\/\/www.knosof.co.uk\/vulnerabilities\/loopcntrl.pdf> Analysis of loop control variables in C\n30. **[^](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-30)**\n    Lee, Sarah. [\"Turing's Halting Problem Explained\"](https:\/\/www.numberanalytics.com\/blog\/ultimate-guide-turing-halting-problem). *www.numberanalytics.com*. Retrieved 2026-01-22.\n31. **[^](https:\/\/en.wikipedia.org\/wiki\/While_loop#cite_ref-31)**\n    [\"What is an infinite loop (endless loop)?\"](https:\/\/www.techtarget.com\/whatis\/definition\/infinite-loop-endless-loop). *WhatIs*. Retrieved 2026-01-22.","meta_canonical":"org,wikipedia!en,\/wiki\/Loop_(statement) s443"}

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Boilerpipe Text	From Wikipedia, the free encyclopedia In computer programming , a loop is a control flow statement that allows code to be executed repeatedly, usually with minor alterations between repetitions. Loops can be used to perform a repeated action on all items in a collection , or to implement a long lived program. Loops are a feature of high-level programming languages . In low-level programming languages the same functionality is achieved using jumps . When a program is compiled to machine code , looping may be achieved using jumps; but some loops can be optimized to run without jumping. [ 1 ] Usually, loops are expected to run for a finite number of iteration. [ citation needed ] Without proper care, loops may accidentally be created that have no possibility of terminating. Such loops are called infinite loops . The problem of determining whether a program contains an infinite loop is known as the halting problem . A conditional loop (also known as an indeterminate loop [ 2 ] ) is a loop that determines whether to terminate based on a logical condition. [ 3 ] These loops are flexible, but there exact behavior can be difficult to reason about. [ 4 ] : 368 A conditional loop is usually composed of two parts: a condition and a body . The condition is a logical statement depending on the state of the program and the body is a block of code that runs as long as the condition holds. [ 3 ] A common misconception is that the execution of the body terminates as soon as the condition does not hold anymore; but this is usually not the case. [ 4 ] : 368 In most programming languages, the condition is checked once for every execution of the body . When the condition is checked is not standardized and some programming languages contain multiple conditional looping structures with different rules about when the condition is assessed. [ citation needed ] A pre-test loop is a conditional loop where the condition is checked before the body is executed. More precisely, the condition is checked and if it holds the body is execute. Afterwards, the condition is checked again, and if it holds the body is executed again. This process repeats until the condition does not hold. Many programming languages call this loop a while loop and refer to it with the keyword while . They are commonly formatted in manner similar to while condition do body repeat Instead of the keywords do and repeat others methods are sometime use to indicate where the body begins and ends, such as curly braces [ 5 ] or whitespace . [ 6 ] For example, the following code fragment first checks whether x is less than five, which it is, so the body is entered. There, x is displayed and then incremented by one. After executing the statements in the body , the condition is checked again, and the loop is executed again. This process repeats until x has the value five. x ← 0 while x < 5 do display( x ) x ← x + 1 repeat Do-While loop flow diagram A post-test loop is a conditional loop where the condition is checked after the body is executed. More precisely, the body is executed and afterwards the condition is checked. If it holds the body is run again and then the condition is checked. This is repeated until the condition does not hold. This is sometimes called a do-while loop due to the syntax used in various programming languages, [ 7 ] although this can be confusing since Fortran and PL/I use the syntax "DO WHILE" for pre-test loops. [ 8 ] [ 9 ] Post-test loops are commonly formatted in manner similar to do body repeat while condition Instead of the keywords do and repeat others methods are sometime use to indicate where the body begins and ends, such as curly braces. [ 10 ] Some languages may use a different naming convention for this type of loop. For example, the Pascal and Lua languages have a " repeat until " loop, which continues to run until the control expression is true and then terminates. [ 11 ] [ 12 ] Three-part for loop [ edit ] Flow diagram of a for loop that prints five asterisks. A three-part for loop , popularized by C, has two additional parts: initialization ( loop variant ), and increment , both of which are blocks of code. The initialization is intended as code that prepares the loop and is run once in the beginning and increment is used to update the state of the program after each iteration of the loop. Otherwise, the three-part for loop is a pre-test loop. They are commonly formatted in manner similar to for initialization , condition , increment do body repeat This syntax came from B and was originally invented by Stephen C. Johnson . [ 13 ] The following C code is an example of a three part loop that prints the numbers from 0 to 4. for ( int i = 0 ; i < 5 ; i ++ ) { printf ( "%d \n " , i ); } Equivalent constructs [ edit ] Assuming there is a function called do_work() that does some work, the following are equivalent. [ citation needed ] do do_work() repeat while condition do_work() while condition do do_work() repeat As long as the continue statement is not used, the above is technically equivalent to the following (though these examples are not typical or modern style used in everyday computers): while true do do_work() if condition is not true then break end if repeat or LOOPSTART: do_work() if condition then goto LOOPSTART end if foreach loops are almost always used to iterate over items in a sequence of elements. An enumeration (also known as an determinate loop [ 2 ] ) is a loop intended to iterate over all the items of a collection. [ 14 ] It is not as flexible as a conditional loop; but it is more predictable. [ citation needed ] For example, it is easier to guarantee that enumerations terminate and they avoid potential off-by-one errors . [ citation needed ] Enumerations can be implemented using an iterator , whether implicitly or explicitly. They are commonly formatted in manner similar to for item in collection body repeat Depending on the programming language, various keywords are used to invoke enumerations. For example, descendants of ALGOL use for , [ 15 ] while descendants of Fortran use do [ 16 ] and COBOL uses PERFORM VARYING . [ 17 ] Enumerations are sometimes called "for loops," for example in Zig and Rust . [ 18 ] [ 19 ] This can be confusing since many of the most popular [ 20 ] programming languages, such as C, C++ , and Java , use that term for the three-part for loop, [ 21 ] [ 22 ] [ 23 ] which is not an enumeration. Other programming languages, such as Perl and C# , avoid this confusion by using the term "foreach loop." [ 24 ] [ 25 ] The order in which the items in the collection are iterated through depends on the programming language. Fortran 95 has a loop, invoked using the keyword FORALL , that is independent of this order. It has the effect of executing each iteration of the loop at the same time. This feature was made obsolescent in Fortran 2018 . [ 26 ] Loops in functional programming [ edit ] In most functional programming languages , recursion is used instead of traditional loops. This is due to the fact that variables are immutable , and therefore the increment step of a loop cannot occur. [ 27 ] To avoid running into stack overflow errors for long loops, functional programming languages implement tail call optimisation , which allows the same stack frame to be used for each iteration of the loop, compiling to effectively the same code as a while or for loop. [ 28 ] Some languages, such as Haskell , have a special syntax known as a list comprehension , which is similar to enumeration, iterating over the contents of a list and transforming it into a new list. A loop counter is a control variable that controls the iterations of a loop. Loop counters change with each iteration of a loop, providing a unique value for each iteration. The loop counter is used to decide when the loop should terminate. It is so named because most uses of this construct result in the variable taking on a range of integer values. A common identifier naming convention is for the loop counter to use the variable names i , j , and k (and so on if needed), [ 29 ] where i would be the most outer loop, j the next inner loop, etc. This style is generally agreed to have originated from the early programming of Fortran [ citation needed ] , where these variable names beginning with these letters were implicitly declared as having an integer type, and so were obvious choices for loop counters that were only temporarily required. The practice dates back further to mathematical notation where indices for sums and multiplications are often i , j , and k . Using terse names for loop counters, like i and j , is discouraged by some since the purpose of the variables is not as clear as if they were given a longer more descriptive name. [ 4 ] : 383–382 Different languages specify different rules for what value the loop counter will hold on termination of its loop, and indeed some hold that it becomes undefined. This permits a compiler to generate code that leaves any value in the loop counter, or perhaps even leaves it unchanged because the loop value was held in a register and never stored in memory. Actual behavior may even vary according to the compiler's optimization settings. Modifying the loop counter within the body of the loop can lead to unexpected consequences. To prevent such problems, some languages make the loop counter immutable . [ citation needed ] However, only overt changes are likely to be detected by the compiler. Situations where the address of the loop counter is passed as an argument to a subroutine , make it very difficult to check because the routine's behavior is in general unknowable to the compiler unless the language supports procedure signatures and argument intents. [ citation needed ] Early exit and continuation [ edit ] Some languages may also provide supporting statements for altering how a loop's iteration proceeds. Common among these are the break statement, which terminates the current loop the program is in, and the continue statement, which skips to the next iteration of the current loop. [ 4 ] : 379 These statements may have other names; For example in Fortran 90 , they are called exit and cycle . [ citation needed ] A loop can also be terminated by returning from the function within which it is being executed. In the case of nested loops, the break and continue statements apply to the inner most loop. Some languages allow loops to be labelled. These statements can then be applied to any of the loops in which the program is nested. outer_loop: (This is a label for the outermost loop) for 1 ≤ i ≤ 2 do for 1 ≤ j ≤ 2 do display(i, j) if i = 2 continue outer_loop end if repeat repeat (This nested loop displays the pairs (1, 1), (1, 2), and (2, 1)) An infinite loop is a loop which never terminates. This can be intentional, or the result of a logic error . Systematically detecting infinite loops is known as the halting problem . [ 30 ] Infinite loops are useful in applications which need to perform a repeated calculation until a program terminates, such as web servers . [ 31 ] Primitive recursive function General recursive function Repeat loop (disambiguation) LOOP (programming language) – a programming language with the property that the functions it can compute are exactly the primitive recursive functions ^ Angelou, Alexandros; Dadaliaris, Antonios; Dossis, Michael; Dimitriou, Georgios (2021-11-26). "Branchless Code Generation for Modern Processor Architectures" . 25th Pan-Hellenic Conference on Informatics . New York, NY, USA: ACM: 300– 305. doi : 10.1145/3503823.3503879 . ISBN 978-1-4503-9555-7 . ^ a b Samanta, Debasis; Sarma, Monalisa (15 June 2023). Joy with Java: Fundamentals of Object Oriented Programming . Cambridge University Press. p. 124. ISBN 978-1-009-21190-1 . ^ a b "Conditional loops - Computational constructs - National 4 Computing Science Revision" . BBC Bitesize . Archived from the original on 19 October 2021 . Retrieved 8 January 2026 . ^ a b c d McConnell, Steve (9 June 2004). Code Complete . Pearson Education. ISBN 978-0-7356-3697-2 . ^ "while Statement (GNU C Language Manual)" . www.gnu.org . Archived from the original on 12 July 2024 . Retrieved 8 January 2026 . ^ "3. An Informal Introduction to Python" . Python documentation . Archived from the original on 31 December 2025 . Retrieved 8 January 2026 . ^ "do...while - JavaScript \| MDN" . MDN Web Docs . 2025-07-08 . Retrieved 2026-01-22 . ^ "DO WHILE (FORTRAN 77 Language Reference)" . docs.oracle.com . Archived from the original on 14 March 2023 . Retrieved 8 January 2026 . ^ "DO command (PL/I)" . www.ibm.com . Archived from the original on 2 March 2025 . Retrieved 22 January 2026 . ^ "do-while Statement (GNU C Language Manual)" . www.gnu.org . Archived from the original on 13 July 2024 . Retrieved 8 January 2026 . ^ "The Repeat..until statement" . www.freepascal.org . Archived from the original on 9 November 2025 . Retrieved 22 January 2026 . ^ "Programming in Lua : 4.3.3" . www.lua.org . Archived from the original on 2 January 2026 . Retrieved 22 January 2026 . ^ Thompson, Ken . VCF East 2019 – Brian Kernighan interviews Ken Thompson . YouTube . Archived from the original on 2021-12-12 . Retrieved 2020-11-16 . I saw Johnson's semicolon version of the for loop and I put that in [B], I stole it. ^ McConnell, Steve (9 June 2004). Code Complete . Pearson Education. p. 367. ISBN 978-0-7356-3697-2 . ^ Wirth, Niklaus (1973). "Preface". Systematic Programming: An Introduction . Prentice-Hall. pp. xiii. ISBN 0138803692 . ^ "DO / END DO" . www.ibm.com . 24 April 2018. Archived from the original on 8 January 2026 . Retrieved 8 January 2026 . ^ "PERFORM with VARYING Phrase" . www.ibm.com . June 2012. Archived from the original on 8 January 2026 . Retrieved 8 January 2026 . ^ "Zig documentation" . ziglang.org . Archived from the original on 4 January 2026 . Retrieved 8 January 2026 . ^ "Looping Through a Collection with for" . rust-lang.org . Archived from the original on 19 December 2025 . Retrieved 8 January 2026 . ^ "TIOBE Index for September 2024" . Archived from the original on January 4, 2026 . Retrieved 2025-12-16 . ^ "for Statement (GNU C Language Manual)" . www.gnu.org . Archived from the original on 13 July 2024 . Retrieved 8 January 2026 . ^ "for statement (C++)" . learn.microsoft.com . Archived from the original on 28 September 2025 . Retrieved 8 January 2026 . ^ "The for Statement (The Java™ Tutorials > Learning the Java Language > Language Basics)" . docs.oracle.com . Archived from the original on 28 December 2025 . Retrieved 8 January 2026 . ^ "Iteration statements -for, foreach, do, and while - C# reference" . learn.microsoft.com . Archived from the original on 28 December 2025 . Retrieved 8 January 2026 . ^ "Perl for Loop" . Perl Tutorial . Archived from the original on 7 June 2025 . Retrieved 8 January 2026 . ^ "FORALL" . Intel . Archived from the original on 1 January 2026 . Retrieved 8 January 2026 . ^ Hinsen, Konrad (2009). "The Promises of Functional Programming" . Computing in Science & Engineering . 11 (4): 86– 90. Bibcode : 2009CSE....11d..86H . doi : 10.1109/mcse.2009.129 . ISSN 1521-9615 . ^ Clinger, William D. (1998). "Proper tail recursion and space efficiency". Proceedings of the ACM SIGPLAN 1998 conference on Programming language design and implementation . New York, NY, USA: ACM. pp. 174– 185. doi : 10.1145/277650.277719 . ISBN 0-89791-987-4 . ^ http://www.knosof.co.uk/vulnerabilities/loopcntrl.pdf Analysis of loop control variables in C ^ Lee, Sarah. "Turing's Halting Problem Explained" . www.numberanalytics.com . Retrieved 2026-01-22 . ^ "What is an infinite loop (endless loop)?" . WhatIs . Retrieved 2026-01-22 .
Markdown	[Jump to content](https://en.wikipedia.org/wiki/While_loop#bodyContent) Main menu Main menu move to sidebar hide Navigation - [Main page](https://en.wikipedia.org/wiki/Main_Page "Visit the main page [z]") - [Contents](https://en.wikipedia.org/wiki/Wikipedia:Contents "Guides to browsing Wikipedia") - [Current events](https://en.wikipedia.org/wiki/Portal:Current_events "Articles related to current events") - [Random article](https://en.wikipedia.org/wiki/Special:Random "Visit a randomly selected article [x]") - [About Wikipedia](https://en.wikipedia.org/wiki/Wikipedia:About "Learn about Wikipedia and how it works") - [Contact us](https://en.wikipedia.org/wiki/Wikipedia:Contact_us "How to contact Wikipedia") Contribute - [Help](https://en.wikipedia.org/wiki/Help:Contents "Guidance on how to use and edit Wikipedia") - [Learn to edit](https://en.wikipedia.org/wiki/Help:Introduction "Learn how to edit Wikipedia") - [Community portal](https://en.wikipedia.org/wiki/Wikipedia:Community_portal "The hub for editors") - [Recent changes](https://en.wikipedia.org/wiki/Special:RecentChanges "A list of recent changes to Wikipedia [r]") - [Upload file](https://en.wikipedia.org/wiki/Wikipedia:File_upload_wizard "Add images or other media for use on Wikipedia") - [Special pages](https://en.wikipedia.org/wiki/Special:SpecialPages "A list of all special pages [q]") [![](https://en.wikipedia.org/static/images/icons/enwiki-25.svg) ![Wikipedia](https://en.wikipedia.org/static/images/mobile/copyright/wikipedia-wordmark-en-25.svg) ![The Free Encyclopedia](https://en.wikipedia.org/static/images/mobile/copyright/wikipedia-tagline-en-25.svg)](https://en.wikipedia.org/wiki/Main_Page) [Search](https://en.wikipedia.org/wiki/Special:Search "Search Wikipedia [f]") Appearance - [Donate](https://donate.wikimedia.org/?wmf_source=donate&wmf_medium=sidebar&wmf_campaign=en.wikipedia.org&uselang=en) - [Create account](https://en.wikipedia.org/w/index.php?title=Special:CreateAccount&returnto=Loop+%28statement%29 "You are encouraged to create an account and log in; however, it is not mandatory") - [Log in](https://en.wikipedia.org/w/index.php?title=Special:UserLogin&returnto=Loop+%28statement%29 "You're encouraged to log in; however, it's not mandatory. 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[o]") ## Contents move to sidebar hide - [(Top)](https://en.wikipedia.org/wiki/While_loop) - [1 Overview](https://en.wikipedia.org/wiki/While_loop#Overview) - [2 Conditional loop](https://en.wikipedia.org/wiki/While_loop#Conditional_loop) Toggle Conditional loop subsection - [2\.1 Pre-test loop](https://en.wikipedia.org/wiki/While_loop#Pre-test_loop) - [2\.2 Post-test loop](https://en.wikipedia.org/wiki/While_loop#Post-test_loop) - [2\.3 Three-part for loop](https://en.wikipedia.org/wiki/While_loop#Three-part_for_loop) - [2\.4 Equivalent constructs](https://en.wikipedia.org/wiki/While_loop#Equivalent_constructs) - [3 Enumeration](https://en.wikipedia.org/wiki/While_loop#Enumeration) - [4 Loops in functional programming](https://en.wikipedia.org/wiki/While_loop#Loops_in_functional_programming) - [5 Loop counter](https://en.wikipedia.org/wiki/While_loop#Loop_counter) - [6 Early exit and continuation](https://en.wikipedia.org/wiki/While_loop#Early_exit_and_continuation) - [7 Infinite loop](https://en.wikipedia.org/wiki/While_loop#Infinite_loop) - [8 See also](https://en.wikipedia.org/wiki/While_loop#See_also) - [9 References](https://en.wikipedia.org/wiki/While_loop#References) Toggle the table of contents # Loop (statement) 25 languages - [Boarisch](https://bar.wikipedia.org/wiki/Schleifn_\(Programmierung\) "Schleifn (Programmierung) – Bavarian") - [Български](https://bg.wikipedia.org/wiki/%D0%A6%D0%B8%D0%BA%D1%8A%D0%BB_\(%D0%BF%D1%80%D0%BE%D0%B3%D1%80%D0%B0%D0%BC%D0%B8%D1%80%D0%B0%D0%BD%D0%B5\) "Цикъл (програмиране) – Bulgarian") - [Català](https://ca.wikipedia.org/wiki/Bucle_\(programaci%C3%B3\) "Bucle (programació) – Catalan") - [Deutsch](https://de.wikipedia.org/wiki/Schleife_\(Programmierung\) "Schleife (Programmierung) – German") - [Español](https://es.wikipedia.org/wiki/Bucle_\(programaci%C3%B3n\) "Bucle (programación) – Spanish") - [Eesti](https://et.wikipedia.org/wiki/Ts%C3%BCkkel_\(programmeerimine\) "Tsükkel (programmeerimine) – Estonian") - [Euskara](https://eu.wikipedia.org/wiki/Begizta_\(programazioa\) "Begizta (programazioa) – Basque") - 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Please help [improve this article](https://en.wikipedia.org/wiki/Special:EditPage/Loop_\(statement\) "Special:EditPage/Loop (statement)") by [adding citations to reliable sources](https://en.wikipedia.org/wiki/Help:Referencing_for_beginners "Help:Referencing for beginners"). Unsourced material may be challenged and removed. Find sources: ["Loop" statement](https://www.google.com/search?as_eq=wikipedia&q=%22Loop%22+statement) – [news](https://www.google.com/search?tbm=nws&q=%22Loop%22+statement+-wikipedia&tbs=ar:1) · [newspapers](https://www.google.com/search?&q=%22Loop%22+statement&tbs=bkt:s&tbm=bks) · [books](https://www.google.com/search?tbs=bks:1&q=%22Loop%22+statement+-wikipedia) · [scholar](https://scholar.google.com/scholar?q=%22Loop%22+statement) · [JSTOR](https://www.jstor.org/action/doBasicSearch?Query=%22Loop%22+statement&acc=on&wc=on) (January 2026) ([Learn how and when to remove this message](https://en.wikipedia.org/wiki/Help:Maintenance_template_removal "Help:Maintenance template removal")) \| In [computer programming](https://en.wikipedia.org/wiki/Computer_programming "Computer programming"), a loop is a [control flow](https://en.wikipedia.org/wiki/Control_flow "Control flow") [statement](https://en.wikipedia.org/wiki/Statement_\(computer_science\) "Statement (computer science)") that allows code to be executed repeatedly, usually with minor alterations between repetitions. Loops can be used to perform a repeated action on all items in a [collection](https://en.wikipedia.org/wiki/Collection_\(abstract_data_type\) "Collection (abstract data type)"), or to implement a long lived program. ## Overview \[[edit](https://en.wikipedia.org/w/index.php?title=Loop_\(statement\)&action=edit&section=1 "Edit section: Overview")\] Loops are a feature of [high-level programming languages](https://en.wikipedia.org/wiki/High-level_programming_languages "High-level programming languages"). In [low-level programming languages](https://en.wikipedia.org/wiki/Low-level_programming_languages "Low-level programming languages") the same functionality is achieved using [jumps](https://en.wikipedia.org/wiki/Control_flow#Jump "Control flow"). When a program is [compiled](https://en.wikipedia.org/wiki/Compiler "Compiler") to [machine code](https://en.wikipedia.org/wiki/Machine_code "Machine code"), looping may be achieved using jumps; but some loops can be [optimized](https://en.wikipedia.org/wiki/Code_optimization "Code optimization") to run without jumping.[\[1\]](https://en.wikipedia.org/wiki/While_loop#cite_note-1) Usually, loops are expected to run for a finite number of iteration.\[[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed "Wikipedia:Citation needed")\] Without proper care, loops may accidentally be created that have no possibility of terminating. Such loops are called [infinite loops](https://en.wikipedia.org/wiki/Infinite_loop "Infinite loop"). The problem of determining whether a program contains an infinite loop is known as the [halting problem](https://en.wikipedia.org/wiki/Halting_problem "Halting problem"). ## Conditional loop \[[edit](https://en.wikipedia.org/w/index.php?title=Loop_\(statement\)&action=edit&section=2 "Edit section: Conditional loop")\] A conditional loop (also known as an indeterminate loop[\[2\]](https://en.wikipedia.org/wiki/While_loop#cite_note-joy-2)) is a loop that determines whether to terminate based on a logical condition.[\[3\]](https://en.wikipedia.org/wiki/While_loop#cite_note-bbc1-3) These loops are flexible, but there exact behavior can be difficult to reason about.[\[4\]](https://en.wikipedia.org/wiki/While_loop#cite_note-codecomplete-4): 368 A conditional loop is usually composed of two parts: a condition and a body. The condition is a logical statement depending on the state of the program and the body is a block of code that runs as long as the condition holds.[\[3\]](https://en.wikipedia.org/wiki/While_loop#cite_note-bbc1-3) A common misconception is that the execution of the body terminates as soon as the condition does not hold anymore; but this is usually not the case.[\[4\]](https://en.wikipedia.org/wiki/While_loop#cite_note-codecomplete-4): 368 In most programming languages, the condition is checked once for every execution of the body. When the condition is checked is not standardized and some programming languages contain multiple conditional looping structures with different rules about when the condition is assessed.\[[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed "Wikipedia:Citation needed")\] ### Pre-test loop \[[edit](https://en.wikipedia.org/w/index.php?title=Loop_\(statement\)&action=edit&section=3 "Edit section: Pre-test loop")\] A pre-test loop is a conditional loop where the condition is checked before the body is executed. More precisely, the condition is checked and if it holds the body is execute. Afterwards, the condition is checked again, and if it holds the body is executed again. This process repeats until the condition does not hold. Many programming languages call this loop a while loop and refer to it with the [keyword](https://en.wikipedia.org/wiki/Reserved_word "Reserved word") while. They are commonly formatted in manner similar to ``` while condition do body repeat ``` Instead of the keywords do and repeat others methods are sometime use to indicate where the body begins and ends, such as [curly braces](https://en.wikipedia.org/wiki/Curly_braces "Curly braces")[\[5\]](https://en.wikipedia.org/wiki/While_loop#cite_note-5) or [whitespace](https://en.wikipedia.org/wiki/Whitespace_characters "Whitespace characters").[\[6\]](https://en.wikipedia.org/wiki/While_loop#cite_note-6) For example, the following code fragment first checks whether x is less than five, which it is, so the body is entered. There, x is displayed and then incremented by one. After executing the statements in the body, the condition is checked again, and the loop is executed again. This process repeats until x has the value five. ``` x ← 0 while x < 5 do display(x) x ← x + 1 repeat ``` ### Post-test loop \[[edit](https://en.wikipedia.org/w/index.php?title=Loop_\(statement\)&action=edit&section=4 "Edit section: Post-test loop")\] [![](https://upload.wikimedia.org/wikipedia/commons/thumb/9/92/Do-while-loop-diagram.svg/250px-Do-while-loop-diagram.svg.png)](https://en.wikipedia.org/wiki/File:Do-while-loop-diagram.svg) Do-While loop flow diagram A post-test loop is a conditional loop where the condition is checked after the body is executed. More precisely, the body is executed and afterwards the condition is checked. If it holds the body is run again and then the condition is checked. This is repeated until the condition does not hold. This is sometimes called a do-while loop due to the syntax used in various programming languages,[\[7\]](https://en.wikipedia.org/wiki/While_loop#cite_note-7) although this can be confusing since [Fortran](https://en.wikipedia.org/wiki/Fortran "Fortran") and [PL/I](https://en.wikipedia.org/wiki/PL/I "PL/I") use the syntax "DO WHILE" for pre-test loops.[\[8\]](https://en.wikipedia.org/wiki/While_loop#cite_note-8)[\[9\]](https://en.wikipedia.org/wiki/While_loop#cite_note-9) Post-test loops are commonly formatted in manner similar to ``` do body repeat while condition ``` Instead of the keywords do and repeat others methods are sometime use to indicate where the body begins and ends, such as curly braces.[\[10\]](https://en.wikipedia.org/wiki/While_loop#cite_note-10) Some [languages](https://en.wikipedia.org/wiki/Programming_language "Programming language") may use a different naming convention for this type of loop. For example, the [Pascal](https://en.wikipedia.org/wiki/Pascal_programming_language "Pascal programming language") and [Lua](https://en.wikipedia.org/wiki/Lua_\(programming_language\) "Lua (programming language)") languages have a "repeat until" loop, which continues to run until the control expression is true and then terminates.[\[11\]](https://en.wikipedia.org/wiki/While_loop#cite_note-11)[\[12\]](https://en.wikipedia.org/wiki/While_loop#cite_note-12) ### Three-part for loop \[[edit](https://en.wikipedia.org/w/index.php?title=Loop_\(statement\)&action=edit&section=5 "Edit section: Three-part for loop")\] [![](https://upload.wikimedia.org/wikipedia/commons/thumb/d/d1/For_loop_example.svg/250px-For_loop_example.svg.png)](https://en.wikipedia.org/wiki/File:For_loop_example.svg) Flow diagram of a for loop that prints five asterisks. A three-part for loop, popularized by C, has two additional parts: [initialization](https://en.wikipedia.org/wiki/Declaration_\(computer_programming\) "Declaration (computer programming)") ([loop variant](https://en.wikipedia.org/wiki/Loop_variant "Loop variant")), and increment, both of which are blocks of code. The initialization is intended as code that prepares the loop and is run once in the beginning and increment is used to update the state of the program after each iteration of the loop. Otherwise, the three-part for loop is a pre-test loop. They are commonly formatted in manner similar to ``` for initialization, condition, increment do body repeat ``` This syntax came from [B](https://en.wikipedia.org/wiki/B_\(programming_language\) "B (programming language)") and was originally invented by [Stephen C. Johnson](https://en.wikipedia.org/wiki/Stephen_C._Johnson "Stephen C. Johnson").[\[13\]](https://en.wikipedia.org/wiki/While_loop#cite_note-ken-13) The following C code is an example of a three part loop that prints the numbers from 0 to 4. ``` for (int i = 0; i < 5; i++) { printf("%d\n", i); } ``` ### Equivalent constructs \[[edit](https://en.wikipedia.org/w/index.php?title=Loop_\(statement\)&action=edit&section=6 "Edit section: Equivalent constructs")\] \| \| \| \|---\|---\| \| [![\[icon\]](https://upload.wikimedia.org/wikipedia/commons/thumb/1/1c/Wiki_letter_w_cropped.svg/20px-Wiki_letter_w_cropped.svg.png)](https://en.wikipedia.org/wiki/File:Wiki_letter_w_cropped.svg) \| This section needs expansion. You can help by [adding missing information](https://en.wikipedia.org/w/index.php?title=Loop_\(statement\)&action=edit&section=). (January 2026) \| Assuming there is a function called do\_work() that does some work, the following are equivalent.\[[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed "Wikipedia:Citation needed")\] As long as the continue statement is not used, the above is technically equivalent to the following (though these examples are not typical or modern style used in everyday computers): ``` while true do do_work() if condition is not true then break end if repeat ``` or ``` LOOPSTART: do_work() if condition then goto LOOPSTART end if ``` ## Enumeration \[[edit](https://en.wikipedia.org/w/index.php?title=Loop_\(statement\)&action=edit&section=7 "Edit section: Enumeration")\] [![](https://upload.wikimedia.org/wikipedia/commons/thumb/1/13/For-Loop-Mint-Programming-Language-Type-2.gif/250px-For-Loop-Mint-Programming-Language-Type-2.gif)](https://en.wikipedia.org/wiki/File:For-Loop-Mint-Programming-Language-Type-2.gif) `foreach` loops are almost always used to iterate over items in a sequence of elements. An enumeration (also known as an determinate loop[\[2\]](https://en.wikipedia.org/wiki/While_loop#cite_note-joy-2)) is a loop intended to iterate over all the items of a collection.[\[14\]](https://en.wikipedia.org/wiki/While_loop#cite_note-14) It is not as flexible as a conditional loop; but it is more predictable.\[[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed "Wikipedia:Citation needed")\] For example, it is easier to guarantee that enumerations [terminate](https://en.wikipedia.org/wiki/Terminate "Terminate") and they avoid potential [off-by-one errors](https://en.wikipedia.org/wiki/Off-by-one_error "Off-by-one error").\[[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed "Wikipedia:Citation needed")\] Enumerations can be implemented using an [iterator](https://en.wikipedia.org/wiki/Iterator "Iterator"), whether implicitly or explicitly. They are commonly formatted in manner similar to ``` for item in collection body repeat ``` Depending on the programming language, various keywords are used to invoke enumerations. For example, descendants of [ALGOL](https://en.wikipedia.org/wiki/ALGOL "ALGOL") use `for`,[\[15\]](https://en.wikipedia.org/wiki/While_loop#cite_note-15) while descendants of [Fortran](https://en.wikipedia.org/wiki/Fortran "Fortran") use `do`[\[16\]](https://en.wikipedia.org/wiki/While_loop#cite_note-16) and [COBOL](https://en.wikipedia.org/wiki/COBOL "COBOL") uses `PERFORM VARYING`.[\[17\]](https://en.wikipedia.org/wiki/While_loop#cite_note-17) Enumerations are sometimes called "for loops," for example in [Zig](https://en.wikipedia.org/wiki/Zig_\(programming_language\) "Zig (programming language)") and [Rust](https://en.wikipedia.org/wiki/Rust_\(programming_language\) "Rust (programming language)").[\[18\]](https://en.wikipedia.org/wiki/While_loop#cite_note-18)[\[19\]](https://en.wikipedia.org/wiki/While_loop#cite_note-19) This can be confusing since many of the most popular[\[20\]](https://en.wikipedia.org/wiki/While_loop#cite_note-20) programming languages, such as C, [C++](https://en.wikipedia.org/wiki/C%2B%2B "C++"), and [Java](https://en.wikipedia.org/wiki/Java_\(programming_language\) "Java (programming language)"), use that term for the three-part for loop,[\[21\]](https://en.wikipedia.org/wiki/While_loop#cite_note-21)[\[22\]](https://en.wikipedia.org/wiki/While_loop#cite_note-22)[\[23\]](https://en.wikipedia.org/wiki/While_loop#cite_note-23) which is not an enumeration. Other programming languages, such as [Perl](https://en.wikipedia.org/wiki/Perl "Perl") and [C\#](https://en.wikipedia.org/wiki/C "C"), avoid this confusion by using the term "foreach loop."[\[24\]](https://en.wikipedia.org/wiki/While_loop#cite_note-24)[\[25\]](https://en.wikipedia.org/wiki/While_loop#cite_note-25) The order in which the items in the collection are iterated through depends on the programming language. [Fortran 95](https://en.wikipedia.org/wiki/Fortran_95 "Fortran 95") has a loop, invoked using the keyword `FORALL`, that is independent of this order. It has the effect of executing each iteration of the loop at the same time. This feature was made obsolescent in [Fortran 2018](https://en.wikipedia.org/wiki/Fortran_2018 "Fortran 2018").[\[26\]](https://en.wikipedia.org/wiki/While_loop#cite_note-26) ## Loops in functional programming \[[edit](https://en.wikipedia.org/w/index.php?title=Loop_\(statement\)&action=edit&section=8 "Edit section: Loops in functional programming")\] \| \| \| \|---\|---\| \| [![\[icon\]](https://upload.wikimedia.org/wikipedia/commons/thumb/1/1c/Wiki_letter_w_cropped.svg/20px-Wiki_letter_w_cropped.svg.png)](https://en.wikipedia.org/wiki/File:Wiki_letter_w_cropped.svg) \| This section needs expansion. You can help by [adding missing information](https://en.wikipedia.org/w/index.php?title=Loop_\(statement\)&action=edit&section=). (January 2026) \| In most [functional programming languages](https://en.wikipedia.org/wiki/Functional_programming "Functional programming"), [recursion](https://en.wikipedia.org/wiki/Recursion_\(computer_science\) "Recursion (computer science)") is used instead of traditional loops. This is due to the fact that variables are [immutable](https://en.wikipedia.org/wiki/Immutable_object "Immutable object"), and therefore the increment step of a loop cannot occur.[\[27\]](https://en.wikipedia.org/wiki/While_loop#cite_note-27) To avoid running into [stack overflow](https://en.wikipedia.org/wiki/Stack_overflow "Stack overflow") errors for long loops, functional programming languages implement [tail call optimisation](https://en.wikipedia.org/wiki/Tail_call "Tail call"), which allows the same [stack frame](https://en.wikipedia.org/wiki/Call_stack "Call stack") to be used for each iteration of the loop, compiling to effectively the same code as a while or for loop.[\[28\]](https://en.wikipedia.org/wiki/While_loop#cite_note-28) Some languages, such as [Haskell](https://en.wikipedia.org/wiki/Haskell "Haskell"), have a special syntax known as a [list comprehension](https://en.wikipedia.org/wiki/List_comprehension "List comprehension"), which is similar to enumeration, iterating over the contents of a list and transforming it into a new list. ## Loop counter \[[edit](https://en.wikipedia.org/w/index.php?title=Loop_\(statement\)&action=edit&section=9 "Edit section: Loop counter")\] A loop counter is a control variable that controls the iterations of a loop. Loop counters change with each iteration of a loop, providing a unique value for each iteration. The loop counter is used to decide when the loop should terminate. It is so named because most uses of this construct result in the variable taking on a range of integer values. A common [identifier naming convention](https://en.wikipedia.org/wiki/Identifier_naming_convention "Identifier naming convention") is for the loop counter to use the variable names i, j, and k (and so on if needed),[\[29\]](https://en.wikipedia.org/wiki/While_loop#cite_note-29) where i would be the most outer loop, j the next inner loop, etc. This style is generally agreed to have originated from the early programming of Fortran\[[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed "Wikipedia:Citation needed")\], where these variable names beginning with these letters were implicitly declared as having an integer type, and so were obvious choices for loop counters that were only temporarily required. The practice dates back further to [mathematical notation](https://en.wikipedia.org/wiki/Mathematical_notation "Mathematical notation") where [indices](https://en.wikipedia.org/wiki/Index_notation "Index notation") for [sums](https://en.wikipedia.org/wiki/Summation "Summation") and [multiplications](https://en.wikipedia.org/wiki/Multiplication "Multiplication") are often i, j, and k. Using terse names for loop counters, like i and j, is discouraged by some since the purpose of the variables is not as clear as if they were given a longer more descriptive name.[\[4\]](https://en.wikipedia.org/wiki/While_loop#cite_note-codecomplete-4): 383–382 Different languages specify different rules for what value the loop counter will hold on termination of its loop, and indeed some hold that it becomes undefined. This permits a [compiler](https://en.wikipedia.org/wiki/Compiler "Compiler") to generate code that leaves any value in the loop counter, or perhaps even leaves it unchanged because the loop value was held in a register and never stored in memory. Actual behavior may even vary according to the compiler's optimization settings. Modifying the loop counter within the body of the loop can lead to unexpected consequences. To prevent such problems, some languages make the loop counter [immutable](https://en.wikipedia.org/wiki/Immutable_object "Immutable object").\[[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed "Wikipedia:Citation needed")\] However, only overt changes are likely to be detected by the compiler. Situations where the address of the loop counter is passed as an argument to a [subroutine](https://en.wikipedia.org/wiki/Subroutine "Subroutine"), make it very difficult to check because the routine's behavior is in general unknowable to the compiler unless the language supports procedure signatures and argument intents.\[[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed "Wikipedia:Citation needed")\] ## Early exit and continuation \[[edit](https://en.wikipedia.org/w/index.php?title=Loop_\(statement\)&action=edit&section=10 "Edit section: Early exit and continuation")\] Some languages may also provide supporting statements for altering how a loop's iteration proceeds. Common among these are the [break](https://en.wikipedia.org/wiki/Break_statement "Break statement") statement, which terminates the current loop the program is in, and the [continue](https://en.wikipedia.org/wiki/Control_flow#Continuation_with_next_iteration "Control flow") statement, which skips to the next iteration of the current loop.[\[4\]](https://en.wikipedia.org/wiki/While_loop#cite_note-codecomplete-4): 379 These statements may have other names; For example in [Fortran 90](https://en.wikipedia.org/wiki/Fortran_90 "Fortran 90"), they are called exit and cycle.\[[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed "Wikipedia:Citation needed")\] A loop can also be terminated by [returning](https://en.wikipedia.org/wiki/Return_statement "Return statement") from the function within which it is being executed. In the case of nested loops, the break and continue statements apply to the inner most loop. Some languages allow loops to be labelled. These statements can then be applied to any of the loops in which the program is nested. ``` outer_loop: (This is a label for the outermost loop) for 1 ≤ i ≤ 2 do for 1 ≤ j ≤ 2 do display(i, j) if i = 2 continue outer_loop end if repeat repeat (This nested loop displays the pairs (1, 1), (1, 2), and (2, 1)) ``` ## Infinite loop \[[edit](https://en.wikipedia.org/w/index.php?title=Loop_\(statement\)&action=edit&section=11 "Edit section: Infinite loop")\] Main article: [Infinite loop](https://en.wikipedia.org/wiki/Infinite_loop "Infinite loop") \| \| \| \|---\|---\| \| [![\[icon\]](https://upload.wikimedia.org/wikipedia/commons/thumb/1/1c/Wiki_letter_w_cropped.svg/20px-Wiki_letter_w_cropped.svg.png)](https://en.wikipedia.org/wiki/File:Wiki_letter_w_cropped.svg) \| This section needs expansion. You can help by [adding missing information](https://en.wikipedia.org/w/index.php?title=Loop_\(statement\)&action=edit&section=). (January 2026) \| An infinite loop is a loop which never terminates. This can be intentional, or the result of a [logic error](https://en.wikipedia.org/wiki/Logic_error "Logic error"). Systematically detecting infinite loops is known as the [halting problem](https://en.wikipedia.org/wiki/Halting_problem "Halting problem").[\[30\]](https://en.wikipedia.org/wiki/While_loop#cite_note-30) Infinite loops are useful in applications which need to perform a repeated calculation until a program terminates, such as [web servers](https://en.wikipedia.org/wiki/Web_servers "Web servers").[\[31\]](https://en.wikipedia.org/wiki/While_loop#cite_note-31) ## See also \[[edit](https://en.wikipedia.org/w/index.php?title=Loop_\(statement\)&action=edit&section=12 "Edit section: See also")\] - [Primitive recursive function](https://en.wikipedia.org/wiki/Primitive_recursive_function "Primitive recursive function") - [General recursive function](https://en.wikipedia.org/wiki/General_recursive_function "General recursive function") - [Repeat loop (disambiguation)](https://en.wikipedia.org/wiki/Repeat_loop_\(disambiguation\) "Repeat loop (disambiguation)") - [LOOP (programming language)](https://en.wikipedia.org/wiki/LOOP_\(programming_language\) "LOOP (programming language)") – a programming language with the property that the functions it can compute are exactly the primitive recursive functions ## References \[[edit](https://en.wikipedia.org/w/index.php?title=Loop_\(statement\)&action=edit&section=13 "Edit section: References")\] 1. [^](https://en.wikipedia.org/wiki/While_loop#cite_ref-1) Angelou, Alexandros; Dadaliaris, Antonios; Dossis, Michael; Dimitriou, Georgios (2021-11-26). ["Branchless Code Generation for Modern Processor Architectures"](https://doi.org/10.1145/3503823.3503879). 25th Pan-Hellenic Conference on Informatics. New York, NY, USA: ACM: 300–305\. [doi](https://en.wikipedia.org/wiki/Doi_\(identifier\) "Doi (identifier)"):[10\.1145/3503823.3503879](https://doi.org/10.1145%2F3503823.3503879). [ISBN](https://en.wikipedia.org/wiki/ISBN_\(identifier\) "ISBN (identifier)") [978-1-4503-9555-7](https://en.wikipedia.org/wiki/Special:BookSources/978-1-4503-9555-7 "Special:BookSources/978-1-4503-9555-7") . 2. ^ [*a](https://en.wikipedia.org/wiki/While_loop#cite_ref-joy_2-0) [b](https://en.wikipedia.org/wiki/While_loop#cite_ref-joy_2-1) Samanta, Debasis; Sarma, Monalisa (15 June 2023). [Joy with Java: Fundamentals of Object Oriented Programming](https://books.google.com/books?id=34GyEAAAQBAJ). Cambridge University Press. p. 124. [ISBN](https://en.wikipedia.org/wiki/ISBN_\(identifier\) "ISBN (identifier)") [978-1-009-21190-1](https://en.wikipedia.org/wiki/Special:BookSources/978-1-009-21190-1 "Special:BookSources/978-1-009-21190-1") . 3. ^ [a](https://en.wikipedia.org/wiki/While_loop#cite_ref-bbc1_3-0) [b](https://en.wikipedia.org/wiki/While_loop#cite_ref-bbc1_3-1) ["Conditional loops - Computational constructs - National 4 Computing Science Revision"](https://web.archive.org/web/20211019111021/https://www.bbc.co.uk/bitesize/guides/zcg9kqt/revision/8). BBC Bitesize. Archived from [the original](https://www.bbc.co.uk/bitesize/guides/zcg9kqt/revision/8) on 19 October 2021. Retrieved 8 January 2026. 4. ^ [a](https://en.wikipedia.org/wiki/While_loop#cite_ref-codecomplete_4-0) [b](https://en.wikipedia.org/wiki/While_loop#cite_ref-codecomplete_4-1) [c](https://en.wikipedia.org/wiki/While_loop#cite_ref-codecomplete_4-2) [d](https://en.wikipedia.org/wiki/While_loop#cite_ref-codecomplete_4-3) McConnell, Steve (9 June 2004). [Code Complete](https://books.google.com/books?id=LpVCAwAAQBAJ). Pearson Education. [ISBN](https://en.wikipedia.org/wiki/ISBN_\(identifier\) "ISBN (identifier)") [978-0-7356-3697-2](https://en.wikipedia.org/wiki/Special:BookSources/978-0-7356-3697-2 "Special:BookSources/978-0-7356-3697-2") . 5. [^](https://en.wikipedia.org/wiki/While_loop#cite_ref-5)* ["while Statement (GNU C Language Manual)"](https://web.archive.org/web/20240712235744/https://www.gnu.org/software/c-intro-and-ref/manual/html_node/while-Statement.html). www.gnu.org. Archived from [the original](https://www.gnu.org/software/c-intro-and-ref/manual/html_node/while-Statement.html) on 12 July 2024. Retrieved 8 January 2026. 6. [^](https://en.wikipedia.org/wiki/While_loop#cite_ref-6) ["3. An Informal Introduction to Python"](https://web.archive.org/web/20251231204216/https://docs.python.org/3/tutorial/introduction.html). Python documentation. Archived from [the original](https://docs.python.org/3/tutorial/introduction.html) on 31 December 2025. Retrieved 8 January 2026. 7. [^](https://en.wikipedia.org/wiki/While_loop#cite_ref-7) ["do...while - JavaScript \\| MDN"](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/do...while). MDN Web Docs. 2025-07-08. Retrieved 2026-01-22. 8. [^](https://en.wikipedia.org/wiki/While_loop#cite_ref-8) ["DO WHILE (FORTRAN 77 Language Reference)"](https://web.archive.org/web/20230314015649/https://docs.oracle.com/cd/E19957-01/805-4939/6j4m0vn8e/index.html). docs.oracle.com. 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[^](https://en.wikipedia.org/wiki/While_loop#cite_ref-11) ["The Repeat..until statement"](https://web.archive.org/web/20251109225700/https://www.freepascal.org/docs-html/ref/refsu60.html). www.freepascal.org. Archived from [the original](https://www.freepascal.org/docs-html/ref/refsu60.html) on 9 November 2025. Retrieved 22 January 2026. 12. [^](https://en.wikipedia.org/wiki/While_loop#cite_ref-12) ["Programming in Lua : 4.3.3"](https://web.archive.org/web/20260102100039/https://www.lua.org/pil/4.3.3.html). www.lua.org. Archived from [the original](https://www.lua.org/pil/4.3.3.html) on 2 January 2026. Retrieved 22 January 2026. 13. [^](https://en.wikipedia.org/wiki/While_loop#cite_ref-ken_13-0) [Thompson, Ken](https://en.wikipedia.org/wiki/Ken_Thompson "Ken Thompson"). [VCF East 2019 – Brian Kernighan interviews Ken Thompson](https://www.youtube.com/watch?v=EY6q5dv_B-o&t=2330). [YouTube](https://en.wikipedia.org/wiki/YouTube "YouTube"). [Archived](https://ghostarchive.org/varchive/youtube/20211212/EY6q5dv_B-o) from the original on 2021-12-12. Retrieved 2020-11-16. "I saw Johnson's semicolon version of the for loop and I put that in \[B\], I stole it." 14. [^](https://en.wikipedia.org/wiki/While_loop#cite_ref-14) McConnell, Steve (9 June 2004). [Code Complete](https://books.google.com/books?id=LpVCAwAAQBAJ&q=code+complete). Pearson Education. p. 367. [ISBN](https://en.wikipedia.org/wiki/ISBN_\(identifier\) "ISBN (identifier)") [978-0-7356-3697-2](https://en.wikipedia.org/wiki/Special:BookSources/978-0-7356-3697-2 "Special:BookSources/978-0-7356-3697-2") . 15. [^](https://en.wikipedia.org/wiki/While_loop#cite_ref-15) [Wirth, Niklaus](https://en.wikipedia.org/wiki/Niklaus_Wirth "Niklaus Wirth") (1973). "Preface". Systematic Programming: An Introduction. Prentice-Hall. pp. xiii. [ISBN](https://en.wikipedia.org/wiki/ISBN_\(identifier\) "ISBN (identifier)") [0138803692](https://en.wikipedia.org/wiki/Special:BookSources/0138803692 "Special:BookSources/0138803692") . 16. [^](https://en.wikipedia.org/wiki/While_loop#cite_ref-16) ["DO / END DO"](https://web.archive.org/web/20260108231419/https://www.ibm.com/docs/en/xl-fortran-linux/16.1.0?topic=directives-do-end-do). www.ibm.com. 24 April 2018. Archived from [the original](https://www.ibm.com/docs/en/xl-fortran-linux/16.1.0?topic=directives-do-end-do) on 8 January 2026. Retrieved 8 January 2026. 17. [^](https://en.wikipedia.org/wiki/While_loop#cite_ref-17) ["PERFORM with VARYING Phrase"](https://web.archive.org/web/20260108231758/https://www.ibm.com/docs/en/i/7.5.0?topic=statement-perform-varying-phrase). www.ibm.com. June 2012. Archived from [the original](https://www.ibm.com/docs/en/i/7.5.0?topic=statement-perform-varying-phrase) on 8 January 2026. Retrieved 8 January 2026. 18. [^](https://en.wikipedia.org/wiki/While_loop#cite_ref-18) ["Zig documentation"](https://web.archive.org/web/20260104121319/https://ziglang.org/documentation/master/#for). ziglang.org. Archived from [the original](https://ziglang.org/documentation/master/#for) on 4 January 2026. Retrieved 8 January 2026. 19. [^](https://en.wikipedia.org/wiki/While_loop#cite_ref-19) ["Looping Through a Collection with for"](https://web.archive.org/web/20251219092527/https://doc.rust-lang.org/stable/book/ch03-05-control-flow.html#looping-through-a-collection-with-for). rust-lang.org. Archived from [the original](https://doc.rust-lang.org/stable/book/ch03-05-control-flow.html#looping-through-a-collection-with-for) on 19 December 2025. Retrieved 8 January 2026. 20. [^](https://en.wikipedia.org/wiki/While_loop#cite_ref-20) ["TIOBE Index for September 2024"](https://web.archive.org/web/20260104151245/https://www.tiobe.com/tiobe-index/). Archived from [the original](https://www.tiobe.com/tiobe-index/) on January 4, 2026. Retrieved 2025-12-16. 21. [^](https://en.wikipedia.org/wiki/While_loop#cite_ref-21) ["for Statement (GNU C Language Manual)"](https://web.archive.org/web/20240713014231/https://www.gnu.org/software/c-intro-and-ref/manual/html_node/for-Statement.html). www.gnu.org. Archived from [the original](https://www.gnu.org/software/c-intro-and-ref/manual/html_node/for-Statement.html) on 13 July 2024. Retrieved 8 January 2026. 22. [^](https://en.wikipedia.org/wiki/While_loop#cite_ref-22) ["for statement (C++)"](https://web.archive.org/web/20250928185930/https://learn.microsoft.com/en-us/cpp/cpp/for-statement-cpp?view=msvc-170). learn.microsoft.com. Archived from [the original](https://learn.microsoft.com/en-us/cpp/cpp/for-statement-cpp?view=msvc-170) on 28 September 2025. Retrieved 8 January 2026. 23. [^](https://en.wikipedia.org/wiki/While_loop#cite_ref-23) ["The for Statement (The Java™ Tutorials \> Learning the Java Language \> Language Basics)"](https://web.archive.org/web/20251228051928/https://docs.oracle.com/javase/tutorial/java/nutsandbolts/for.html). docs.oracle.com. Archived from [the original](https://docs.oracle.com/javase/tutorial/java/nutsandbolts/for.html) on 28 December 2025. Retrieved 8 January 2026. 24. [^](https://en.wikipedia.org/wiki/While_loop#cite_ref-24) ["Iteration statements -for, foreach, do, and while - C\# reference"](https://web.archive.org/web/20251228021319/https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/statements/iteration-statements). learn.microsoft.com. Archived from [the original](https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/statements/iteration-statements) on 28 December 2025. Retrieved 8 January 2026. 25. [^](https://en.wikipedia.org/wiki/While_loop#cite_ref-25) ["Perl for Loop"](https://web.archive.org/web/20250607160051/https://www.perltutorial.org/perl-for-loop/). Perl Tutorial. Archived from [the original](https://www.perltutorial.org/perl-for-loop/) on 7 June 2025. Retrieved 8 January 2026. 26. [^](https://en.wikipedia.org/wiki/While_loop#cite_ref-26) ["FORALL"](https://web.archive.org/web/20260101223642/https://www.intel.com/content/www/us/en/docs/fortran-compiler/developer-guide-reference/2025-2/forall.html). Intel. Archived from [the original](https://www.intel.com/content/www/us/en/docs/fortran-compiler/developer-guide-reference/2025-2/forall.html) on 1 January 2026. Retrieved 8 January 2026. 27. [^](https://en.wikipedia.org/wiki/While_loop#cite_ref-27) Hinsen, Konrad (2009). ["The Promises of Functional Programming"](https://doi.org/10.1109/mcse.2009.129). Computing in Science & Engineering. 11 (4): 86–90\. [Bibcode](https://en.wikipedia.org/wiki/Bibcode_\(identifier\) "Bibcode (identifier)"):[2009CSE....11d..86H](https://ui.adsabs.harvard.edu/abs/2009CSE....11d..86H). [doi](https://en.wikipedia.org/wiki/Doi_\(identifier\) "Doi (identifier)"):[10\.1109/mcse.2009.129](https://doi.org/10.1109%2Fmcse.2009.129). [ISSN](https://en.wikipedia.org/wiki/ISSN_\(identifier\) "ISSN (identifier)") [1521-9615](https://search.worldcat.org/issn/1521-9615). 28. [^](https://en.wikipedia.org/wiki/While_loop#cite_ref-28) Clinger, William D. (1998). "Proper tail recursion and space efficiency". Proceedings of the ACM SIGPLAN 1998 conference on Programming language design and implementation. New York, NY, USA: ACM. pp. 174–185\. [doi](https://en.wikipedia.org/wiki/Doi_\(identifier\) "Doi (identifier)"):[10\.1145/277650.277719](https://doi.org/10.1145%2F277650.277719). [ISBN](https://en.wikipedia.org/wiki/ISBN_\(identifier\) "ISBN (identifier)") [0-89791-987-4](https://en.wikipedia.org/wiki/Special:BookSources/0-89791-987-4 "Special:BookSources/0-89791-987-4") . 29. [^](https://en.wikipedia.org/wiki/While_loop#cite_ref-29) <http://www.knosof.co.uk/vulnerabilities/loopcntrl.pdf> Analysis of loop control variables in C 30. [^](https://en.wikipedia.org/wiki/While_loop#cite_ref-30) Lee, Sarah. ["Turing's Halting Problem Explained"](https://www.numberanalytics.com/blog/ultimate-guide-turing-halting-problem). www.numberanalytics.com. Retrieved 2026-01-22. 31. [^](https://en.wikipedia.org/wiki/While_loop#cite_ref-31) ["What is an infinite loop (endless loop)?"](https://www.techtarget.com/whatis/definition/infinite-loop-endless-loop). WhatIs. 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Readable Markdown	From Wikipedia, the free encyclopedia In [computer programming](https://en.wikipedia.org/wiki/Computer_programming "Computer programming"), a loop is a [control flow](https://en.wikipedia.org/wiki/Control_flow "Control flow") [statement](https://en.wikipedia.org/wiki/Statement_\(computer_science\) "Statement (computer science)") that allows code to be executed repeatedly, usually with minor alterations between repetitions. Loops can be used to perform a repeated action on all items in a [collection](https://en.wikipedia.org/wiki/Collection_\(abstract_data_type\) "Collection (abstract data type)"), or to implement a long lived program. Loops are a feature of [high-level programming languages](https://en.wikipedia.org/wiki/High-level_programming_languages "High-level programming languages"). In [low-level programming languages](https://en.wikipedia.org/wiki/Low-level_programming_languages "Low-level programming languages") the same functionality is achieved using [jumps](https://en.wikipedia.org/wiki/Control_flow#Jump "Control flow"). When a program is [compiled](https://en.wikipedia.org/wiki/Compiler "Compiler") to [machine code](https://en.wikipedia.org/wiki/Machine_code "Machine code"), looping may be achieved using jumps; but some loops can be [optimized](https://en.wikipedia.org/wiki/Code_optimization "Code optimization") to run without jumping.[\[1\]](https://en.wikipedia.org/wiki/While_loop#cite_note-1) Usually, loops are expected to run for a finite number of iteration.\[[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed "Wikipedia:Citation needed")\] Without proper care, loops may accidentally be created that have no possibility of terminating. Such loops are called [infinite loops](https://en.wikipedia.org/wiki/Infinite_loop "Infinite loop"). The problem of determining whether a program contains an infinite loop is known as the [halting problem](https://en.wikipedia.org/wiki/Halting_problem "Halting problem"). A conditional loop (also known as an indeterminate loop[\[2\]](https://en.wikipedia.org/wiki/While_loop#cite_note-joy-2)) is a loop that determines whether to terminate based on a logical condition.[\[3\]](https://en.wikipedia.org/wiki/While_loop#cite_note-bbc1-3) These loops are flexible, but there exact behavior can be difficult to reason about.[\[4\]](https://en.wikipedia.org/wiki/While_loop#cite_note-codecomplete-4): 368 A conditional loop is usually composed of two parts: a condition and a body. The condition is a logical statement depending on the state of the program and the body is a block of code that runs as long as the condition holds.[\[3\]](https://en.wikipedia.org/wiki/While_loop#cite_note-bbc1-3) A common misconception is that the execution of the body terminates as soon as the condition does not hold anymore; but this is usually not the case.[\[4\]](https://en.wikipedia.org/wiki/While_loop#cite_note-codecomplete-4): 368 In most programming languages, the condition is checked once for every execution of the body. When the condition is checked is not standardized and some programming languages contain multiple conditional looping structures with different rules about when the condition is assessed.\[[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed "Wikipedia:Citation needed")\] A pre-test loop is a conditional loop where the condition is checked before the body is executed. More precisely, the condition is checked and if it holds the body is execute. Afterwards, the condition is checked again, and if it holds the body is executed again. This process repeats until the condition does not hold. Many programming languages call this loop a while loop and refer to it with the [keyword](https://en.wikipedia.org/wiki/Reserved_word "Reserved word") while. They are commonly formatted in manner similar to ``` while condition do body repeat ``` Instead of the keywords do and repeat others methods are sometime use to indicate where the body begins and ends, such as [curly braces](https://en.wikipedia.org/wiki/Curly_braces "Curly braces")[\[5\]](https://en.wikipedia.org/wiki/While_loop#cite_note-5) or [whitespace](https://en.wikipedia.org/wiki/Whitespace_characters "Whitespace characters").[\[6\]](https://en.wikipedia.org/wiki/While_loop#cite_note-6) For example, the following code fragment first checks whether x is less than five, which it is, so the body is entered. There, x is displayed and then incremented by one. After executing the statements in the body, the condition is checked again, and the loop is executed again. This process repeats until x has the value five. ``` x ← 0 while x < 5 do display(x) x ← x + 1 repeat ``` [![](https://upload.wikimedia.org/wikipedia/commons/thumb/9/92/Do-while-loop-diagram.svg/250px-Do-while-loop-diagram.svg.png)](https://en.wikipedia.org/wiki/File:Do-while-loop-diagram.svg) Do-While loop flow diagram A post-test loop is a conditional loop where the condition is checked after the body is executed. More precisely, the body is executed and afterwards the condition is checked. If it holds the body is run again and then the condition is checked. This is repeated until the condition does not hold. This is sometimes called a do-while loop due to the syntax used in various programming languages,[\[7\]](https://en.wikipedia.org/wiki/While_loop#cite_note-7) although this can be confusing since [Fortran](https://en.wikipedia.org/wiki/Fortran "Fortran") and [PL/I](https://en.wikipedia.org/wiki/PL/I "PL/I") use the syntax "DO WHILE" for pre-test loops.[\[8\]](https://en.wikipedia.org/wiki/While_loop#cite_note-8)[\[9\]](https://en.wikipedia.org/wiki/While_loop#cite_note-9) Post-test loops are commonly formatted in manner similar to ``` do body repeat while condition ``` Instead of the keywords do and repeat others methods are sometime use to indicate where the body begins and ends, such as curly braces.[\[10\]](https://en.wikipedia.org/wiki/While_loop#cite_note-10) Some [languages](https://en.wikipedia.org/wiki/Programming_language "Programming language") may use a different naming convention for this type of loop. For example, the [Pascal](https://en.wikipedia.org/wiki/Pascal_programming_language "Pascal programming language") and [Lua](https://en.wikipedia.org/wiki/Lua_\(programming_language\) "Lua (programming language)") languages have a "repeat until" loop, which continues to run until the control expression is true and then terminates.[\[11\]](https://en.wikipedia.org/wiki/While_loop#cite_note-11)[\[12\]](https://en.wikipedia.org/wiki/While_loop#cite_note-12) ### Three-part for loop \[[edit](https://en.wikipedia.org/w/index.php?title=Loop_\(statement\)&action=edit&section=5 "Edit section: Three-part for loop")\] [![](https://upload.wikimedia.org/wikipedia/commons/thumb/d/d1/For_loop_example.svg/250px-For_loop_example.svg.png)](https://en.wikipedia.org/wiki/File:For_loop_example.svg) Flow diagram of a for loop that prints five asterisks. A three-part for loop, popularized by C, has two additional parts: [initialization](https://en.wikipedia.org/wiki/Declaration_\(computer_programming\) "Declaration (computer programming)") ([loop variant](https://en.wikipedia.org/wiki/Loop_variant "Loop variant")), and increment, both of which are blocks of code. The initialization is intended as code that prepares the loop and is run once in the beginning and increment is used to update the state of the program after each iteration of the loop. Otherwise, the three-part for loop is a pre-test loop. They are commonly formatted in manner similar to ``` for initialization, condition, increment do body repeat ``` This syntax came from [B](https://en.wikipedia.org/wiki/B_\(programming_language\) "B (programming language)") and was originally invented by [Stephen C. Johnson](https://en.wikipedia.org/wiki/Stephen_C._Johnson "Stephen C. Johnson").[\[13\]](https://en.wikipedia.org/wiki/While_loop#cite_note-ken-13) The following C code is an example of a three part loop that prints the numbers from 0 to 4. ``` for (int i = 0; i < 5; i++) { printf("%d\n", i); } ``` ### Equivalent constructs \[[edit](https://en.wikipedia.org/w/index.php?title=Loop_\(statement\)&action=edit&section=6 "Edit section: Equivalent constructs")\] Assuming there is a function called do\_work() that does some work, the following are equivalent.\[[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed "Wikipedia:Citation needed")\] As long as the continue statement is not used, the above is technically equivalent to the following (though these examples are not typical or modern style used in everyday computers): ``` while true do do_work() if condition is not true then break end if repeat ``` or ``` LOOPSTART: do_work() if condition then goto LOOPSTART end if ``` [![](https://upload.wikimedia.org/wikipedia/commons/thumb/1/13/For-Loop-Mint-Programming-Language-Type-2.gif/250px-For-Loop-Mint-Programming-Language-Type-2.gif)](https://en.wikipedia.org/wiki/File:For-Loop-Mint-Programming-Language-Type-2.gif) foreach loops are almost always used to iterate over items in a sequence of elements. An enumeration (also known as an determinate loop[\[2\]](https://en.wikipedia.org/wiki/While_loop#cite_note-joy-2)) is a loop intended to iterate over all the items of a collection.[\[14\]](https://en.wikipedia.org/wiki/While_loop#cite_note-14) It is not as flexible as a conditional loop; but it is more predictable.\[[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed "Wikipedia:Citation needed")\] For example, it is easier to guarantee that enumerations [terminate](https://en.wikipedia.org/wiki/Terminate "Terminate") and they avoid potential [off-by-one errors](https://en.wikipedia.org/wiki/Off-by-one_error "Off-by-one error").\[[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed "Wikipedia:Citation needed")\] Enumerations can be implemented using an [iterator](https://en.wikipedia.org/wiki/Iterator "Iterator"), whether implicitly or explicitly. They are commonly formatted in manner similar to ``` for item in collection body repeat ``` Depending on the programming language, various keywords are used to invoke enumerations. For example, descendants of [ALGOL](https://en.wikipedia.org/wiki/ALGOL "ALGOL") use `for`,[\[15\]](https://en.wikipedia.org/wiki/While_loop#cite_note-15) while descendants of [Fortran](https://en.wikipedia.org/wiki/Fortran "Fortran") use `do`[\[16\]](https://en.wikipedia.org/wiki/While_loop#cite_note-16) and [COBOL](https://en.wikipedia.org/wiki/COBOL "COBOL") uses `PERFORM VARYING`.[\[17\]](https://en.wikipedia.org/wiki/While_loop#cite_note-17) Enumerations are sometimes called "for loops," for example in [Zig](https://en.wikipedia.org/wiki/Zig_\(programming_language\) "Zig (programming language)") and [Rust](https://en.wikipedia.org/wiki/Rust_\(programming_language\) "Rust (programming language)").[\[18\]](https://en.wikipedia.org/wiki/While_loop#cite_note-18)[\[19\]](https://en.wikipedia.org/wiki/While_loop#cite_note-19) This can be confusing since many of the most popular[\[20\]](https://en.wikipedia.org/wiki/While_loop#cite_note-20) programming languages, such as C, [C++](https://en.wikipedia.org/wiki/C%2B%2B "C++"), and [Java](https://en.wikipedia.org/wiki/Java_\(programming_language\) "Java (programming language)"), use that term for the three-part for loop,[\[21\]](https://en.wikipedia.org/wiki/While_loop#cite_note-21)[\[22\]](https://en.wikipedia.org/wiki/While_loop#cite_note-22)[\[23\]](https://en.wikipedia.org/wiki/While_loop#cite_note-23) which is not an enumeration. Other programming languages, such as [Perl](https://en.wikipedia.org/wiki/Perl "Perl") and [C\#](https://en.wikipedia.org/wiki/C "C"), avoid this confusion by using the term "foreach loop."[\[24\]](https://en.wikipedia.org/wiki/While_loop#cite_note-24)[\[25\]](https://en.wikipedia.org/wiki/While_loop#cite_note-25) The order in which the items in the collection are iterated through depends on the programming language. [Fortran 95](https://en.wikipedia.org/wiki/Fortran_95 "Fortran 95") has a loop, invoked using the keyword `FORALL`, that is independent of this order. It has the effect of executing each iteration of the loop at the same time. This feature was made obsolescent in [Fortran 2018](https://en.wikipedia.org/wiki/Fortran_2018 "Fortran 2018").[\[26\]](https://en.wikipedia.org/wiki/While_loop#cite_note-26) ## Loops in functional programming \[[edit](https://en.wikipedia.org/w/index.php?title=Loop_\(statement\)&action=edit&section=8 "Edit section: Loops in functional programming")\] In most [functional programming languages](https://en.wikipedia.org/wiki/Functional_programming "Functional programming"), [recursion](https://en.wikipedia.org/wiki/Recursion_\(computer_science\) "Recursion (computer science)") is used instead of traditional loops. This is due to the fact that variables are [immutable](https://en.wikipedia.org/wiki/Immutable_object "Immutable object"), and therefore the increment step of a loop cannot occur.[\[27\]](https://en.wikipedia.org/wiki/While_loop#cite_note-27) To avoid running into [stack overflow](https://en.wikipedia.org/wiki/Stack_overflow "Stack overflow") errors for long loops, functional programming languages implement [tail call optimisation](https://en.wikipedia.org/wiki/Tail_call "Tail call"), which allows the same [stack frame](https://en.wikipedia.org/wiki/Call_stack "Call stack") to be used for each iteration of the loop, compiling to effectively the same code as a while or for loop.[\[28\]](https://en.wikipedia.org/wiki/While_loop#cite_note-28) Some languages, such as [Haskell](https://en.wikipedia.org/wiki/Haskell "Haskell"), have a special syntax known as a [list comprehension](https://en.wikipedia.org/wiki/List_comprehension "List comprehension"), which is similar to enumeration, iterating over the contents of a list and transforming it into a new list. A loop counter is a control variable that controls the iterations of a loop. Loop counters change with each iteration of a loop, providing a unique value for each iteration. The loop counter is used to decide when the loop should terminate. It is so named because most uses of this construct result in the variable taking on a range of integer values. A common [identifier naming convention](https://en.wikipedia.org/wiki/Identifier_naming_convention "Identifier naming convention") is for the loop counter to use the variable names i, j, and k (and so on if needed),[\[29\]](https://en.wikipedia.org/wiki/While_loop#cite_note-29) where i would be the most outer loop, j the next inner loop, etc. This style is generally agreed to have originated from the early programming of Fortran\[[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed "Wikipedia:Citation needed")\], where these variable names beginning with these letters were implicitly declared as having an integer type, and so were obvious choices for loop counters that were only temporarily required. The practice dates back further to [mathematical notation](https://en.wikipedia.org/wiki/Mathematical_notation "Mathematical notation") where [indices](https://en.wikipedia.org/wiki/Index_notation "Index notation") for [sums](https://en.wikipedia.org/wiki/Summation "Summation") and [multiplications](https://en.wikipedia.org/wiki/Multiplication "Multiplication") are often i, j, and k. Using terse names for loop counters, like i and j, is discouraged by some since the purpose of the variables is not as clear as if they were given a longer more descriptive name.[\[4\]](https://en.wikipedia.org/wiki/While_loop#cite_note-codecomplete-4): 383–382 Different languages specify different rules for what value the loop counter will hold on termination of its loop, and indeed some hold that it becomes undefined. This permits a [compiler](https://en.wikipedia.org/wiki/Compiler "Compiler") to generate code that leaves any value in the loop counter, or perhaps even leaves it unchanged because the loop value was held in a register and never stored in memory. Actual behavior may even vary according to the compiler's optimization settings. Modifying the loop counter within the body of the loop can lead to unexpected consequences. To prevent such problems, some languages make the loop counter [immutable](https://en.wikipedia.org/wiki/Immutable_object "Immutable object").\[[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed "Wikipedia:Citation needed")\] However, only overt changes are likely to be detected by the compiler. Situations where the address of the loop counter is passed as an argument to a [subroutine](https://en.wikipedia.org/wiki/Subroutine "Subroutine"), make it very difficult to check because the routine's behavior is in general unknowable to the compiler unless the language supports procedure signatures and argument intents.\[[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed "Wikipedia:Citation needed")\] ## Early exit and continuation \[[edit](https://en.wikipedia.org/w/index.php?title=Loop_\(statement\)&action=edit&section=10 "Edit section: Early exit and continuation")\] Some languages may also provide supporting statements for altering how a loop's iteration proceeds. Common among these are the [break](https://en.wikipedia.org/wiki/Break_statement "Break statement") statement, which terminates the current loop the program is in, and the [continue](https://en.wikipedia.org/wiki/Control_flow#Continuation_with_next_iteration "Control flow") statement, which skips to the next iteration of the current loop.[\[4\]](https://en.wikipedia.org/wiki/While_loop#cite_note-codecomplete-4): 379 These statements may have other names; For example in [Fortran 90](https://en.wikipedia.org/wiki/Fortran_90 "Fortran 90"), they are called exit and cycle.\[[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed "Wikipedia:Citation needed")\] A loop can also be terminated by [returning](https://en.wikipedia.org/wiki/Return_statement "Return statement") from the function within which it is being executed. In the case of nested loops, the break and continue statements apply to the inner most loop. Some languages allow loops to be labelled. These statements can then be applied to any of the loops in which the program is nested. ``` outer_loop: (This is a label for the outermost loop) for 1 ≤ i ≤ 2 do for 1 ≤ j ≤ 2 do display(i, j) if i = 2 continue outer_loop end if repeat repeat (This nested loop displays the pairs (1, 1), (1, 2), and (2, 1)) ``` An infinite loop is a loop which never terminates. This can be intentional, or the result of a [logic error](https://en.wikipedia.org/wiki/Logic_error "Logic error"). Systematically detecting infinite loops is known as the [halting problem](https://en.wikipedia.org/wiki/Halting_problem "Halting problem").[\[30\]](https://en.wikipedia.org/wiki/While_loop#cite_note-30) Infinite loops are useful in applications which need to perform a repeated calculation until a program terminates, such as [web servers](https://en.wikipedia.org/wiki/Web_servers "Web servers").[\[31\]](https://en.wikipedia.org/wiki/While_loop#cite_note-31) - [Primitive recursive function](https://en.wikipedia.org/wiki/Primitive_recursive_function "Primitive recursive function") - [General recursive function](https://en.wikipedia.org/wiki/General_recursive_function "General recursive function") - [Repeat loop (disambiguation)](https://en.wikipedia.org/wiki/Repeat_loop_\(disambiguation\) "Repeat loop (disambiguation)") - [LOOP (programming language)](https://en.wikipedia.org/wiki/LOOP_\(programming_language\) "LOOP (programming language)") – a programming language with the property that the functions it can compute are exactly the primitive recursive functions 1. 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