Swapping through pointers

swap gets two pointers whose arrows lead back into main's frame. Writing through *x and *y changes a and b themselves.

Without pointers, swap would only get copies and main would never see the change.

#include <stdio.h>

void swap(int *x, int *y) {
    int tmp = *x;
    *x = *y;
    *y = tmp;
}

int main(void) {
    int a = 1;
    int b = 2;
    swap(&a, &b);
    printf("a = %d, b = %d\n", a, b);
    return 0;
}

Output:

a = 2, b = 1

From the lesson: Pointers