/* fact.cpp
 * Computes the factorial of a number
 *
 * The factorial of a number N is denoted by N!.
 * N! = 1 * 2 * (N - 1) * N
 *
 * By definition  0! is 1
 */
 
#include <cstdlib>
#include <iostream>

using namespace std;

long double factorial(int fact);

int main(int argc, char *argv[])
{
    int fact;
    cout << "Enter a non-negative number less than 30" << endl;  
    cin >> fact;
    if(fact < 0 || fact > 30) {
        cout << "Value out of Range" << endl;
        system("PAUSE");
        exit(1);
    } 
    cout << fixed << factorial(fact) << endl;
    system("PAUSE");
    return EXIT_SUCCESS;
}

long double factorial(int fact){
    if(0 == fact){
        return 1;
    }
    long double product = 1;
    for(int i = 1; i <= fact; i++){
        product *= i;
    }
    return product;
}