#include  "library.h"

// this time we plot a graph of starting value against length
// of sequence, to see if we can make out a pattern. We do see
// the beginning of a pattern, but not enough of it

int collatz(const int start)
{ int count = 0;
  int val = start;
  while (val != 1)
  { if (val % 2 == 0)
      val = val / 2;
    else
      val = val * 3 + 1;
    count = count + 1; }
  return count; }

void main()
{ make_window(700, 600);
  set_pen_width(3);
  set_pen_color(color::red);
  int n = 1;
  while (n < 7000)
  { const double k = collatz(n);
    move_to(n, 600-k);
    draw_point();
    n = n + 1; } }