When it appears in a programming language, which of the following are possible while loop scenarios

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 used in everyday computers):

while (true) { do_work(); if (!condition) break; }

or

LOOPSTART: do_work(); if (condition) goto LOOPSTART;

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 Print factorial

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);

Do-while(0) statements are also commonly used in C macros as a way to wrap multiple statements into a regular (as opposed to compound) statement. It makes a semicolon needed after the macro, providing a more function-like appearance for simple parsers and programmers as well as avoiding the scoping problem with if. It is recommended in CERT C Coding Standard rule PRE10-C.[1]

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

Fortran 90 and later does not have a do-while construct either, but it does have a while loop construct which uses the keywords "do while" and is thus actually the same as the for loop.[2]

program FactorialProg integer :: counter = 5 integer :: factorial = 1 factorial = factorial * counter counter = counter - 1 do while (counter > 0) ! Truth value is tested before the loop 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); //============================================// // The below function does the same as above. // //============================================// int counter = 5; int factorial = 1; while (counter > 0){ factorial *= counter--; /* Multiply, then decrement. */ } System.out.println("The factorial of 5 is " + factorial);

JavaScript

let counter = 5; // Declaring two variables, counter and factorial let factorial = 1; do { factorial *= counter--; //What will be looped } while (counter > 0); //The looping conditions console.log(factorial); //Showing the result

[3]

Kotlin

var counter = 5 var factorial = 1 //These line of code is almost the same as the above JavaScript codes, the only difference is the keyword that shows the results do { factorial *= counter-- } while (counter > 0) println("Factorial of 5 is $factorial")

[4]

Pascal

Pascal does not have a do/while; instead, it has a repeat/until. As mentioned in the introduction, one can consider a repeat/until to be equivalent to a 'do code while not expression' construct.

factorial := 1; counter := 5; repeat factorial := factorial * counter; counter := counter - 1; // In Object Pascal one may use dec (counter); until counter = 0;

PHP

$counter = 5; $factorial = 1; do { $factorial *= $counter--; } while ($counter > 0); echo $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.

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 and later:[5]

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)

• Control flow
• For loop
• Foreach
• Repeat loop (disambiguation)
• While loop

1. ^ "C multi-line macro: do/while(0) vs scope block". Stack Overflow.
2. ^ "Microsoft visual basic". msdn.microsoft.com. Retrieved 21 January 2016.
3. ^ "do...while". MDN Web Docs.
4. ^ "Control Flow: if, when, for, while - Kotlin Programming Language". Kotlin.
5. ^ "Control Flow — The Swift Programming Language (Swift 5.3)". docs.swift.org.

• do {...} while (0) in C macros