// Author:  Keith Shomper
// Date:    11/4/03
// Purpose: To demonstrate a recursive program

#include <iostream>

using namespace std;

int factorial(int n);

int main() {
	int   n, f;

	// prompt the user for the value of n 
	cout << "What number would you like to compute the factorial for?  ";
	cin  >> n;

	f = factorial(n);

	// Display the result
	if (f > 0) {
		cout << n << "! is " << f << endl;
	}

	return 0;
}

int factorial(int n) {
	if ( n < 0) {
		cerr << "Error:  Factorial not defined for negative number " << n << endl;
		return 0;
	} else if (n == 0) {
		return 1;
	} else {
		return n * factorial(n-1);
	}
}