do-while loop

Executes a statement repeatedly, until the value of expression becomes false. The test takes place after each iteration.

Syntax


attr(optional) `do` statement `while (` expression `)` `;`

attr(C++11)	-	any number of attributes
expression	-	any expression which is contextually convertible to bool. This expression is evaluated after each iteration, and if it yields false, the loop is exited.
statement	-	any statement, typically a compound statement, which is the body of the loop

Explanation

statement is always executed at least once, even if expression always yields false. If it should not execute in this case, while or for loop may be used.

If the execution of the loop needs to be terminated at some point, break statement can be used as terminating statement.

If the execution of the loop needs to be continued at the end of the loop body, continue statement can be used as shortcut.

Notes

As part of the C++ forward progress guarantee, the behavior is undefined if a loop that has no observable behavior (does not make calls to I/O functions, access volatile objects, or perform atomic or synchronization operations) does not terminate. Compilers are permitted to remove such loops.

Keywords

do, while

Example

Run this code

#include <iostream>
#include <algorithm>
#include <string>

int main()
{
    int j = 2;
    do { // compound statement is the loop body
        j += 2;
        std::cout << j << " ";
    } while (j < 9);
    std::cout << '\n';
    // common situation where do-while loop is used
    std::string s = "aba";
    std::sort(s.begin(), s.end());
    do std::cout << s << '\n'; // expression statement is the loop body
    while(std::next_permutation(s.begin(), s.end()));
}

Output:

4 6 8 10
aab
aba
baa

Language
Headers
Freestanding and hosted implementations
Named requirements
Language support library
Concepts library (C++20)
Diagnostics library
Utilities library
Strings library
Containers library
Algorithms library
Iterators library
Numerics library
Input/output library
Localizations library
Regular expressions library (C++11)
Atomic operations library (C++11)
Thread support library (C++11)
Filesystem library (C++17)
Technical Specifications