///////    File fac.C    ///////
// factorial function computes n! for non-negative n
/* version 1 */
#include <iostream.h>

int factorial(int n)
{ int ans = 1;
      while (n > 1)
      {    ans = ans * n;       
           n = n - 1;
      } 
      return(ans);
}

int main()
{    cout << "Please enter n :";
     int n;        // declaration 
     cin >> n;     // input from keyboard
     if ( n >= 0 )
         cout << "factorial(" << n << ")="
              << factorial(n) << "\n";
     else
         cerr << "Undefined: factorial of a negative number\n";
     return(0);
}