// factorialr.cpp
#include <iostream>

using namespace std;

// Function for calculating factorial:
unsigned long long factorial(unsigned short int n) {
  // Define variables:
  long long f; // For calculating result
  unsigned short int i; // Iterational value
  // Initialise:
  if (n > 0) f = n; // If calculating factorial of n >= 1 result should be n * (n - 1) ... * 2 * 1;
  else f = 1;   // If calculating factorial of 0 result should be 1:
  i = n;
  // Calculation:
  while (i-- > 1) { f = f * (i); }
  return f; // Return result
}

int main()
{
  unsigned short int n;
  cout << "Find factorial of (enter positive integer): ";
  cin >> n;
  cout << "Answer: " << n << "! = " << factorial(n) << endl;
  return 0;
}