Vòng lặp do while

Bản mẫu:Loop constructs Trong hầu hết ngôn ngữ lập trình máy tính, một vòng lặp do while (tiếng Anh: do while loop) là một câu lệnh luồng điều khiển để thực thi một khối lệnh ít nhất một lần, và sau đó lặp lại việc thực thi khối đó, hay không, tùy thuộc vào điều kiện boolean ở cuối khối đó. do { do_work(); } while (condition); thì tương đương với(==/===) do_work(); while (condition) { do_work(); } hay là while (true) { do_work(); if (!condition) break; } hoặc LOOPSTART: do_work(); if (condition) goto LOOPSTART; Chương trình ví dụ sau tính toán giai thừa của 5 bằng cách dùng cú pháp của ngôn ngữ tương ứng cho một vòng lặpdo-while. var counter:int = 5; var factorial:int = 1; do { factorial *= counter--; /* Multiply, then decrement. */ } while (counter > 0); trace(factorial); 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 trước kia (như GW-BASIC) dùng cú pháp WHILE/WEND. Còn BASIC mới hơn như PowerBASIC cho phép dùng cả cấu trúc WHILE/WEND lẫn DO/LOOP, với cú pháp như DO WHILE/LOOP, DO UNTIL/LOOP, DO/LOOP WHILE, DO/LOOP UNTIL, và DO/LOOP. Mã nguồn BASIC điển hình như sau: 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 int counter = 5; int factorial = 1; do { factorial *= counter--; /* Multiply, then decrement. */ } while (counter > 0); System.Console.WriteLine(factorial); int counter = 5; int factorial = 1; do { factorial *= counter--; /* Multiply, then decrement. */ } while (counter > 0); printf("factorial of 5 is %d\n", factorial); int counter = 5; int factorial = 1; do { factorial *= counter--; } while (counter > 0); std::cout<<"factorial of 5 is "<<factorial<<std::endl; factorial = 1; count = 10; do { factorial *= count--; } while (count > 1); writeOutput(factorial); int counter = 5; int factorial = 1; do { factorial *= counter--; // Multiply, then decrement. } while (counter > 0); writeln("factorial of 5 is ", factorial); 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 int counter = 5; int factorial = 1; do { factorial *= counter--; /* Multiply, then decrement. */ } while (counter > 0); System.out.println("The factorial of 5 is " + factorial); var counter = 5; var factorial = 1; do { factorial *= counter--; } while (counter > 0); console.log(factorial); var counter = 5 var factorial = 1 do { factorial *= counter-- }while(counter > 0) println("Factorial of 5 is $factorial") 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 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, cũng như các hiện thực khác của Scheme, dùng "named-let" như một cách thông dụng để hiện thực vòng lặp: #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. )) counter = 10 factorial = 2 begin factorial *= counter counter -= 2 end while counter > 1 puts factorial | counter factorial | counter:= 5. factorial:= 1. [counter > 0] whileTrue: [factorial:= factorial * counter. counter:= counter - 1]. Transcript show: factorial printString 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) 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 While loop Repeat loop (disambiguation) ^ “Microsoft visual basic”. msdn.microsoft.com. Truy cập ngày 21 tháng 1 năm 2016. ^ “Mozilla Developer Network Documentation - The Do While Loop in JavaScript”. ^ “Kotlin Control Flow - While - Kotlin Programming Language”. do {...} while (0) in C macros