#!/usr/bin/perl

use CGI;

$q = new CGI; 

print $q->header, $q->start_html;

$message = $q->param('message'); # retrieve state 
$n1      = $q->param('n1'); 
$n2      = $q->param('n2'); 
$good    = $q->param('good'); 
$total   = $q->param('total'); 

if ($message) { # is state not empty? 

  $answer  = $q->param('answer'); # read user input 

  $feedback = "The answer was wrong."; 
  if ($answer == $n1 + $n2) {
    $good += 1; 
    $feedback = "The answer was right."; 
  } 

  $total += 1; 

  $n1 = int(rand(100))-50; 
  $n2 = int(rand(100))-50;   

  $question = "What is $n1 + $n2?"; 

  $message = "$feedback ($good/$total) $question"; 
  
} else { # new user (state is empty: initialize state) 
  $n1 = int(rand(100))-50; 
  $n2 = int(rand(100))-50;   
  $good = 0; 
  $total = 0; 
  $question = "What is $n1 + $n2?"; 
  $message = "Welcome to the game! ($good/$total) $question"; 
} 

# report state (message), store state (hidden fields), get ready for more input 

print qq{

  <form>
    $message <p> 

    Type your answer here: <input type="text" name="answer"> <p> 

    <input type="hidden" name="n1" value="$n1"> 
    <input type="hidden" name="n2" value="$n2"> 
    <input type="hidden" name="message" value="$message"> 
    <input type="hidden" name="good" value="$good"> 
    <input type="hidden" name="total" value="$total"> 

    When ready press <input type="submit" value="Proceed"> 
  </form> 

};

print $q->end_html;