// test_factorial_long.c  the simplest example of a recursive function
//                   a recursive function is a function that calls itself
// external
// 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) 
#include "factorial_long.h"
#include <stdio.h>

int main()
{
  printf("test_factorial_long.c using long int, note overflow\n");
  printf(" 0!=%ld \n", factorial_long(0));   // Yes, 0! is one
  printf(" 1!=%ld \n", factorial_long(1l));  // Yes, "C" would convert 1 to 1l
  printf(" 2!=%ld \n", factorial_long(2l));  // because of function prototype
  printf(" 3!=%ld \n", factorial_long(3l));  // coming from factorial_long.h
  printf(" 4!=%ld \n", factorial_long(4l));
  printf(" 5!=%ld \n", factorial_long(5l));
  printf(" 6!=%ld \n", factorial_long(6l));
  printf(" 7!=%ld \n", factorial_long(7l));
  printf(" 8!=%ld \n", factorial_long(8l));
  printf(" 9!=%ld \n", factorial_long(9l));
  printf("10!=%ld \n", factorial_long(10l));
  printf("11!=%ld \n", factorial_long(11l));
  printf("12!=%ld \n", factorial_long(12l));
  printf("13!=%ld \n", factorial_long(13l));
  printf("14!=%ld \n", factorial_long(14l));
  printf("15!=%ld \n", factorial_long(15l));
  printf("16!=%ld \n", factorial_long(16l));
  printf("17!=%ld \n", factorial_long(17l));
  printf("18!=%ld \n", factorial_long(18l));
  printf("19!=%ld \n", factorial_long(19l));
  printf("20!=%ld \n", factorial_long(20l));
  printf("21!=%ld \n", factorial_long(21l)); /* expect a problem with */
  printf("22!=%ld \n", factorial_long(22l)); /* integer overflow      */

  return 0;
}

/* output of execution, with comments, is:
test_factorial_long.c using long int, note overflow
 0!=1 
 1!=1 
 2!=2 
 3!=6 
 4!=24 
 5!=120 
 6!=720 
 7!=5040 
 8!=40320 
 9!=362880 
10!=3628800 
11!=39916800 
12!=479001600 
13!=6227020800 
14!=87178291200 
15!=1307674368000 
16!=20922789888000 
17!=355687428096000 
18!=6402373705728000 
19!=121645100408832000 
20!=2432902008176640000 
21!=-4249290049419214848 wrong and obvious if you check your results 
22!=-1250660718674968576 
*/