Swap two variables using pointers. Call By Reference

swap.c

#include <stdio.h>

void swap(int *a1, int *b1);

int main()
{
    int a = 4, b = 5;
    printf("a = %d b = %d\n", a, b);
    swap(&a, &b);
    printf("a = %d b = %d\n", a, b);
    return 0;
}

void swap(int *a1, int *b1)
{
    *a1 = *a1 + *b1;
    *b1 = *a1 - *b1;
    *a1 = *a1 - *b1;

    printf("%d %d\n", *a1, *b1);

}