swap.c

void swap(int a, int b, int* ref1, int* ref2) {
    *ref2 = a;
    *ref1 = b;
}

int subtract(int a, int b) {
    if(b == 0) return a + 1;
    return a + subtract(a, b - 1);
}


int main() {
    int a = 5, b = 10;
    swap(a, b, &a, &b);
    printf("%d\n%d\n", a,b);
    printf("%d\n", subtract(a,b));
}