#include  <library.h>

/* The Collatz sequence. Starting from any number N:
     if N is even, divide it by two
     if N is odd, multiply it by three and add one
   carry on until it reaches 1

   Nobody knows if there are any numbers for which the
   sequence never reaches one
*/


// one - just print the sequence

void print_collatz_from(const int n)
{ print(n);
  print(" ");
  if (n == 1)
    return;
  else if (n % 2 == 1)
    print_collatz_from(3*n+1);
  else
    print_collatz_from(n/2); }


// two - find out how long the sequence is without printing it

int length_collatz_from(const int n)
{ if (n == 1)
    return 1;
  else if (n % 2 == 1)
  { const int rest = length_collatz_from(3*n+1); 
    return 1 + rest; }
  else
  { const int rest = length_collatz_from(n/2); 
    return 1 + rest; } }


// main tests both

void main()
{ while (true)
  { print("\nStarting point: ");
    const int start = read_int();
    print_collatz_from(start);
    print("\n length = ");
    print(length_collatz_from(start));
    print("\n"); } }