/* this one is a bit more complex. It can count
   in both directions, and that isn't always useful. */

#include "library.h"

/* start and end specify the range of numbers to be counted,
   and don't change as the function is doing its job. X
   records what point it is at now. It is a bit annoying
   because look at main, it doesn't seem reasonable to
   have to say the 30 twice. */

void count_from_to(int start, int end, int x)
{ if (start<=end) 
  { if (x<=end)
    { print(x);
      newline();
      count_from_to(start, end, x+1); } }
  else
  { if (x>=end)
    { print(x);
      newline();
      count_from_to(start, end, x-1); } } }

void main()
{ count_from_to(30, 10, 30); }

/* That version evolved easily from where we were before,
   but with hindsight we can make something nicer: */

void count_from_to(int start, int end)
{ print(start);
  new_line();
  if (start<end)
    count_from_to(start+1, end);
  if (end>start)
    count_from_to(start-1, end); }

/* That got rid of the pesky X */