#include <iostream>
#include <cstdlib>
using namespace std;

int factorial(int n);

int main()
{
	cout << "The factorial of 4 is " << factorial(4) << ".\n";
	int i = factorial(5);
	cout << "The factorial of 5 is " << i << ".\n";
	return EXIT_SUCCESS;
}

int factorial(int n)
{
	if (n < 0) {
		cerr << "argument " << n << " can't be negative.\n";
		return 0;
	}

	int f = 1;

	for (int i = 1; i <= n; ++i) {
		f *= i;
	}

	return f;	//Create a copy of f and return it.
}