//
// CS 202 demonstration program 03
// Written by Dave Williams for 9/16/03 class
//
// Program to demonstrate a recursive functions to calculate factorials
//

unsigned long int Factorial(int);

#include <iostream.h> 
#include <stdlib.h>  
#include <math.h> 

int main()   
{   

   int a;
     
   cout << "\n\nCompute the factorial of an integer using recursion.";   
   
   do
   {
      cout << "\n\n\n\nInput a positive integer (0 to quit): ";   
      cin >> a;
      
      a = abs(a);         // forces the input to be positive

      if (a == 0)         // quit if commanded to do so
         exit(0);
         
      if (a > 20)
         cout << "\nCan't do that - it's too large!";
         
      else
         cout << "\nThe value of " << a << "! = " << Factorial(a);
   
   } while(1);
      
   return 0;       
}


unsigned long int Factorial(int a) 
{
   if (a == 0)
      return 1;
   else
      return (a * Factorial(a-1));
}