C While Loop

A loop repeats a block of code many times. The while loop checks the condition first, and runs the body while it is true. Use it when you do not know how many times to repeat.

Syntax

while (condition) {
    // code to repeat
}

Print numbers 1 to 5

#include <stdio.h>

int main(void) {
    int i = 1;

    while (i <= 5) {
        printf("%d\n", i);
        i++;
    }
    return 0;
}

Output:

The three steps are: set the start value (i = 1), check the condition (i <= 5) and change the value (i++). If you forget the last step, the loop never ends.

Sum of digits of a number

#include <stdio.h>

int main(void) {
    int n = 4825, sum = 0;

    while (n > 0) {
        sum += n % 10;   // last digit
        n /= 10;         // remove last digit
    }
    printf("Sum = %d\n", sum);
    return 0;
}

Output:

Infinite loop

A condition which is always true makes a loop that never stops. We stop it with break.

#include <stdio.h>

int main(void) {
    int count = 0;

    while (1) {
        count++;
        if (count == 3) break;
    }
    printf("Stopped at %d\n", count);
    return 0;
}

Output:

Next: C Do While Loop.

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