What is the return value of f(p,p), if the value of p is initialized to 5 before the call? Note that the first parameter is passed by reference, whereas the second parameter is passed by value.
int f (int &x, int c) {
    c = c – 1;
    if (c==0) return 1;
    x = x + 1;
    return f(x,c) * x;
}