void swap(int *p, int *q) {
   int temp = *p;                  // change the actual values of a and b
   *p = *q;
   *q = temp;
}

int main(void) {
   int a = 5, b = 7;
   swap(&a, &b);
   printf("a = %d, b = %d\n", a, b);  // a and b now successfully swapped
   return 0;
}