#include <iostream>
using namespace std;
int multiply(int x, int y);
int main()
{
cout << "3 * 7 = " << multiply(3, 7) << endl;
cout << "3 * 0 = " << multiply(3, 0) << endl;
cout << "0 * 3 = " << multiply(0, 3) << endl;
cout << "3 * -5 = " << multiply(3, -5) << endl;
cout << "-3 * 6 = " << multiply(-3, 6) << endl;
return 0;
}
int multiply(int x, int y)
{
if (y > 0)
return (x + multiply(x, y - 1));
if (y < 0)
return -multiply(x, -y);
return 0;
}
/*
run:
3 * 7 = 21
3 * 0 = 0
0 * 3 = 0
3 * -5 = -15
-3 * 6 = -18
*/