//
// Program:  factorial
//
// Purpose:  test recursive function for computing n factorial.
//
// Input:
//   non-negative integer N from standard input.
// Output:
//   N factorial printed to standard output.
//
#include <iostream.h>
#include <stdlib.h>

// Pre:  n >= 0.
// Post:  returns n-factorial.
int factorial(const int n)
{
  if (n == 0)
    return 1;
  else
    return n * factorial(n-1);
}

// Main program.
int main(void)
{
  int num;
  cout << "Enter a non-negative integer:  \n";
  cin >> num;
  if (num < 0)
    {
      cout << "Number must not be negative.\n";
      return EXIT_FAILURE;
    }
  cout << "factorial(" << num << ") = " << factorial(num) << endl;
  return EXIT_SUCCESS;
}