Hint

#include <stdio.h>

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

int main() {
    int x, y;
    x = 7;
    y = 8;
    swap(&x, &y);
    printf("x = %d si y = %d\n", x, y);
    return 0;
}