The Do/While Loop
The do/while loop is a variant of the while loop. This loop will execute the code block once , before checking if the condition is true. Then it will repeat the loop as long as the condition is true.
Syntax
do {
// code block to be executed
}
while ( condition );Note
The semicolon ; after the while condition is required!
Do/While Example
The example below uses a do/while loop. The loop will always be executed at least once, even if the condition is false, because the code block is executed before the condition is tested.
Example
int i = 0;
do {
cout << i << "\n";
i++;
}
while (i < 5);Do not forget to increase the variable used in the condition ( i++ ), otherwise the loop will never end!
Condition is False from the Start
In the example above, the condition i < 5 was true at the beginning, so the loop executed multiple times. But what if the condition is false right from the start?
In the example below, the variable i starts at 10 , so the condition i < 5 is false immediately - yet the do/while loop still runs once:
Example
int i = 10;
do {
cout << "i is " << i << "\n";
i++;
} while (i < 5);Summary
The do/while loop always runs at least once, even if the condition is already false. This is different from a regular while loop, which would skip the loop entirely if the condition is false at the start.
This behavior makes do/while useful when you want to ensure something happens at least once, like showing a message or asking for user input.
Practical Example: User Input
This example keeps asking the user to enter a positive number. The loop stops when the user enters 0 or a negative number:
Example
int number;
do {
cout << "Enter a positive number: ";
cin >> number;
} while (number > 0);