do-while loop

< cpp‎ | language

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


[edit] 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

[edit] Explanation

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

If the execution of the loop needs to be terminated at some point, a 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, a continue statement can be used as shortcut.

[edit] 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.

[edit] Keywords

do, while

[edit] Example

#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()));


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[edit] See also

C documentation for do-while