/* 

simple_factorial.c 

Author: W. M. Farmer
Revised: December 1, 2009

Description: Three simple implementations of the factorial function.

*/

#include <stdio.h>

int fact_rec(int n) {
  if (n == 0) 
    return 1;
  else
    return fact_rec(n - 1) * n;
}

int fact_tail_rec_aux(int n, int accum) {
  if (n == 0) 
    return accum;
  else
    return fact_tail_rec_aux(n - 1, accum * n);
}

int fact_tail_rec(int n) {
  return fact_tail_rec_aux(n, 1);
}

int fact_iter(int n) {
  int accum = 1;
  while (n != 0) {
    accum = accum * n;
    n = n - 1;
  }
  return accum;      
}

int main() 
{
  int n = 4;
  printf("fact_rec(%d)      = %d\n", n, fact_rec(n));
  printf("fact_tail_rec(%d) = %d\n", n, fact_tail_rec(n));
  printf("fact_iter(%d)     = %d\n", n, fact_iter(n));
  return 0;
}