Do while loop - wikipedia Do while loop Do While loop flow diagram Loop constructs Do while loop While loop For loop Foreach loop Infinite loop Control flow In most computer programming languages, a do while loop is a control flow statement that executes a block of code at least once, and then repeatedly executes the block, or not, depending on a given boolean condition at the end of the block. The do while construct consists of a process symbol and a condition. First, the code within the block is executed, and then the condition is evaluated. If the condition is true the code within the block is executed again. This repeats until the condition becomes false. Because do while loops check the condition after the block is executed, the control structure is often also known as a post-test loop. Contrast with the while loop, which tests the condition before the code within the block is executed, the do - while loop is an exit - condition loop. This means that the code must always be executed first and then the expression or test condition is evaluated. If it is true, the code executes the body of the loop again. This process is repeated as long as the expression evaluates to true. If the expression is false, the loop terminates and control transfers to the statement following the do - while loop. In other words, whereas a while loop sets the truth of a statement as a condition precedent for the code 's execution, a do - while loop provides for the action 's ongoing execution subject to defeasance by the condition 's falsity, which falsity ( i.e., the truth of the condition 's negation ) is set as a condition subsequent. It is possible, and in some cases desirable, for the condition to always evaluate to true, creating an infinite loop. When such a loop is created intentionally, there is usually another control structure ( such as a break statement ) that allows termination of the loop. Some languages may use a different naming convention for this type of loop. For example, the Pascal language has a `` repeat until '' loop, which continues to run until the control expression is true ( and then terminates ) -- whereas a `` while '' loop runs while the control expression is true ( and terminates once the expression becomes false ). Contents 1 Equivalent constructs 2 Demonstrating do while loops 2.1 ActionScript 3 2.2 Ada 2.3 BASIC 2.4 C# 2.5 C 2.6 C++ 2.7 CFScript 2.8 D 2.9 Fortran 2.10 Java 2.11 JavaScript 2.12 Kotlin 2.13 PL / I 2.14 Python 2.15 Racket 2.16 Ruby 2.17 Smalltalk 2.18 Swift 2.19 Visual Basic. NET 3 See also 4 References 5 External links Equivalent constructs do ( do_work ( ) ; ) while ( condition ) ; is equivalent to do_work ( ) ; while ( condition ) ( do_work ( ) ; ) In this manner, the do... while loop saves the initial `` loop priming '' with do_work ( ) ; on the line before the while loop. 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 ) : while ( true ) ( do_work ( ) ; if ( ! condition ) break ; ) or LOOPSTART : do_work ( ) ; if ( condition ) goto LOOPSTART ; Demonstrating do while loops These example programs calculate the factorial of 5 using their respective languages ' syntax for a do - while loop. ActionScript 3 var counter : int = 5 ; var factorial : int = 1 ; do ( factorial * = counter -- ; / * Multiply, then decrement. * / ) while ( counter > 0 ) ; trace ( factorial ) ; Ada The Wikibook Ada_Programming has a page on the topic of : Control with Ada. Integer_Text_IO ; procedure Factorial is Counter : Integer : = 5 ; Factorial : Integer : = 1 ; begin loop Factorial : = Factorial * Counter ; Counter : = Counter - 1 ; exit when Counter = 0 ; end loop ; Ada. Integer_Text_IO. Put ( Factorial ) ; end Factorial ; BASIC Early BASICs ( such as GW - BASIC ) used the syntax WHILE / WEND. Modern BASICs such as PowerBASIC provide both WHILE / WEND and DO / LOOP structures, with syntax such as DO WHILE / LOOP, DO UNTIL / LOOP, DO / LOOP WHILE, DO / LOOP UNTIL, and DO / LOOP ( without outer testing, but with a conditional EXIT LOOP somewhere inside the loop ). Typical BASIC source code : Dim factorial As Integer Dim counter As Integer factorial = 1 counter = 5 Do factorial = factorial * counter counter = counter - 1 Loop While counter > 0 C# int counter = 5 ; int factorial = 1 ; do ( factorial * = counter -- ; / * Multiply, then decrement. * / ) while ( counter > 0 ) ; System. Console. WriteLine ( factorial ) ; C int counter = 5 ; int factorial = 1 ; do ( factorial * = counter -- ; / * Multiply, then decrement. * / ) while ( counter > 0 ) ; printf ( `` factorial of 5 is % d \n '', factorial ) ; C++ int counter = 5 ; int factorial = 1 ; do ( factorial * = counter -- ; ) while ( counter > 0 ) ; std : : cout < < `` factorial of 5 is `` < < factorial < < std : : endl ; CFScript factorial = 1 ; count = 10 ; do ( factorial * = count -- ; ) while ( count > 1 ) ; writeOutput ( factorial ) ; D int counter = 5 ; int factorial = 1 ; do ( factorial * = counter -- ; / / Multiply, then decrement. ) while ( counter > 0 ) ; writeln ( `` factorial of 5 is ``, factorial ) ; Fortran With legacy FORTRAN 77 there is no DO - WHILE construct but the same effect can be achieved with GOTO : INTEGER CNT, FACT CNT = 5 FACT = 1 1 CONTINUE FACT = FACT * CNT CNT = CNT - 1 IF ( CNT. GT. 0 ) GOTO 1 PRINT *, FACT END With Fortran 90 and later, the do - while loop is actually the same as the for loop. program FactorialProg integer : : counter = 5 integer : : factorial = 1 factorial = factorial * counter counter = counter - 1 do while ( counter > 0 ) factorial = factorial * counter counter = counter - 1 end do print *, factorial end program FactorialProg Java int counter = 5 ; int factorial = 1 ; do ( factorial * = counter -- ; / * Multiply, then decrement. * / ) while ( counter > 0 ) ; System. out. println ( `` the factorial of 5 is `` + factorial ) ; JavaScript var counter = 5 ; var factorial = 1 ; do ( factorial * = counter -- ; ) while ( counter > 0 ) ; console. log ( factorial ) ; Kotlin var counter = 5 var factorial = 1 do ( factorial * = counter -- ) while ( counter > 0 ) println ( `` Factorial of 5 is $ factorial '' ) PL / I The PL / I DO statement subsumes the functions of the post-test loop ( do until ), the pre-test loop ( do while ), and the for loop. All functions can be included in a single statement. The example shows only the `` do until '' syntax. declare counter fixed initial ( 5 ) ; declare factorial fixed initial ( 1 ) ; do until ( counter < = 0 ) ; factorial = factorial * counter ; counter = counter - 1 ; end ; put ( factorial ) ; Python Python lacks a specific do while flow control construct. However, the equivalent may be constructed out of a while loop with a break. counter = 5 factorial = 1 while True : factorial * = counter counter - = 1 if counter = = 0 : break print ( factorial ) Racket In Racket, as in other Scheme implementations, a `` named - let '' is a popular way to implement loops : # lang racket ( define counter 5 ) ( define factorial 1 ) ( let loop ( ) ( set ! factorial ( * factorial counter ) ) ( set ! counter ( sub1 counter ) ) ( when ( > counter 0 ) ( loop ) ) ) ( displayln factorial ) Compare this with the first example of the while loop example for Racket. Be aware that a named let can also take arguments. Racket and Scheme also provide a proper do loop. ( define ( factorial n ) ( do ( ( counter n ( - counter 1 ) ) ( result 1 ( * result counter ) ) ) ( ( = counter 0 ) result ) ; Stop condition and return value. ; The body of the do - loop is empty. ) ) Ruby counter = 10 factorial = 2 begin factorial * = counter counter - = 2 end while counter > 1 puts factorial Smalltalk counter factorial counter : = 5. factorial : = 1. ( counter > 0 ) whileTrue : ( factorial : = factorial * counter. counter : = counter - 1 ). Transcript show : factorial printString Swift Swift 2. x : var counter = 5 var factorial = 1 repeat ( factorial * = counter counter - = 1 ) while counter > 0 print ( factorial ) Swift 1. x : var counter = 5 var factorial = 1 do ( factorial * = counter counter - = 1 ) while counter > 0 println ( factorial ) Visual Basic. NET Dim counter As Integer = 5 Dim factorial As Integer = 1 Do factorial * = counter counter - = 1 Loop While counter > 0 Console. WriteLine ( factorial ) See also Control flow For loop Foreach While loop Repeat loop ( disambiguation ) References Jump up ^ `` Microsoft visual basic ''. msdn.microsoft.com. Retrieved 21 January 2016. Jump up ^ `` Mozilla Developer Network Documentation - The Do While Loop in JavaScript ''. Jump up ^ `` Kotlin Control Flow - While - Kotlin Programming Language ''. External links do (... ) while ( 0 ) in C macros Retrieved from `` https://en.wikipedia.org/w/index.php?title=Do_while_loop&oldid=798334468 '' Categories : Control flow Articles with example Fortran code Articles with example Racket code Hidden categories : Articles with example Ada code Articles with example C code Articles with example Pascal code Articles with example Perl code Talk Contents About Wikipedia Català Čeština Deutsch Español Euskara 한국어 Hrvatski 日本 語 Српски / srpski 中文 Edit links This page was last edited on 1 September 2017, at 08 : 43. Text is available under the Creative Commons Attribution - ShareAlike License ; additional terms may apply. By using this site, you agree to the Terms of Use and Privacy Policy. Wikipedia ® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization. About Wikipedia

Question: the loop which execute once before condition is checked
Answer: post-test loop