/* =========================================

   Filename:  collatz_sequence.c
   Filedate:  February 25, 2007

   Input a positive integer  n.  If it's even,
   divide by 2.  If it's odd, multiply by 3 and
   add 1.  Repeat until you get a 1.

   Note:  It was conjectured by L. Collatz in 1937
   that the sequence always halts, i.e., you eventually
   reach 1.  As of 2006, the conjecture remains 
   unresolved.  Thwaites has offered
   a prize of 1000 English pounds for a solution.

   =========================================  */

#include<stdio.h>
#include<stdlib.h>

int main() {

  int i;
  int current_value;
  int no_terms = 1;

  printf("Input a positive integer:\n");
  scanf("%d", &current_value);

  do {
    printf("Current value is: %d\n",current_value);
    if (current_value%2 == 0) {
      current_value = current_value/2;
    }
    else {
      current_value = 3*current_value + 1;
    }
    no_terms++;
  } while(current_value != 1);

  printf("Reached the value 1 after %d steps.\n", no_terms);
  return(0);
}