C Break and Continue

Sometimes a loop must stop before its condition becomes false, or skip one round. break and continue do exactly that.

break

break leaves the loop at once; the program continues after the loop. It is useful when you have found what you were looking for.

#include <stdio.h>

int main(void) {
    int numbers[] = {4, 9, 15, 22, 8};
    for (int i = 0; i < 5; i++) {
        if (numbers[i] > 10) {
            printf("First number above 10: %d (position %d)\n", numbers[i], i);
            break;
        }
    }
    return 0;
}

First number above 10: 15 (position 2)

You have already seen break in switch, where it ends the switch. Inside a loop it ends the loop.

continue

continue skips the rest of the current round and goes on with the next one.

#include <stdio.h>

int main(void) {
    for (int i = 1; i <= 10; i++) {
        if (i % 3 == 0) {
            continue;          // skip multiples of 3
        }
        printf("%d ", i);
    }
    printf("\n");
    return 0;
}

1 2 4 5 7 8 10 

In a for loop, continue still runs the step (i++). In a while loop it jumps straight to the condition, so make sure the variable is changed before the continue, or the loop never ends.

An input loop with break

A loop that runs "forever" and stops with break is a common pattern for reading input until a stop value:

#include <stdio.h>

int main(void) {
    int total = 0, n;
    while (1) {
        printf("Number (0 to stop): ");
        if (scanf("%d", &n) != 1 || n == 0) {
            break;
        }
        total += n;
    }
    printf("\nTotal: %d\n", total);
    return 0;
}

5
12
0

Number (0 to stop): Number (0 to stop): Number (0 to stop): 
Total: 17

while (1) repeats forever because 1 is always true; the break is the only way out. The program also stops when the input is not a number, because scanf then does not return 1.

Nested loops

break and continue affect only the innermost loop they are in. To leave two loops at once, use a flag variable that the outer loop checks, or put the loops in a function and return.

Practice exercises

1. Print the numbers from 1 to 50, but stop at the first one divisible by both 7 and 5.
2. Print all numbers from 1 to 20 except the multiples of 4, using continue.
3. Read numbers until the user types a negative one, then print how many were read.