// factorial_long.c  the simplest example of a recursive function
//                   a recursive function is a function that calls itself

long int factorial_long(long int n) // n! is n factorial = 1*2*...*(n-1)*n
{
  if( n <= 1 ) return 1;            // must have a way to stop recursion
  return n * factorial_long(n-1);   // factorial calls factorial with n-1
}                                   // n * (n-1) * (n-2) * ... * (1)
                                    // note: "C" makes 1 be 1l  long