#!/usr/bin/perl -w

use strict;

use constant MIN => 0;
use constant MAX => 40000;

my($low, $high, $mid) = (MIN, MAX);

print "Think of a number between $low and $high\n";

while(1) {
  $mid = int(($low + $high) / 2);

  last if $low >= $high;

  print "How about $mid? Is it (l)ow, (h)igh or (c)orrect? : ";

  my $answer = lc(substr <STDIN>, 0, 1);

  $answer eq 'c' ? last             :
  $answer eq 'l' ? $low  = $mid + 1 :
  $answer eq 'h' ? $high = $mid - 1 :
  print "bad input\n";
}

print "The number you are thinking of is $mid!\n";