`do`-`while` loop

Conditionally executes a statement repeatedly (at least once).

Syntax

attr (optional) do statement while ( expression );

attr	-	(since C++11) any number of attributes
expression	-	an expression
statement	-	a statement (typically a compound statement)

Explanation

When control reaches a do statement, its statement will be executed unconditionally.

Every time statement finishes its execution, expression will be evaluated and contextually converted to bool. If the result is true, statement will be executed again.

If the loop needs to be terminated within statement, a break statement can be used as terminating statement.

If the current iteration needs to be terminated within statement, a continue statement can be used as shortcut.

Notes

As part of the C++ forward progress guarantee, the behavior is undefined if a loop that is not a trivial infinite loop(since C++26) without observable behavior does not terminate. Compilers are permitted to remove such loops.

Keywords

do, while

Example

#include <algorithm>
#include <iostream>
#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