int Fact(int N)
// ---------------------------------------------------
// Computes the factorial of a nonnegative integer.
// Precondition: N must be greater than or equal to 0.
// Postcondition: Returns the factorial of N; N is
// unchanged.
// ---------------------------------------------------
{
   if (N == 0)
      return 1;
   else
      return N * Fact(N-1);
}  // end Fact