Here's an example of this transformational logic.

Start with this program, to reinforce our knowledge of sessions:

<? session_start();
   if ($message){
     $num+=1;
   } else {
     $message = "This is my program";
     session_register ("message");
     $num = -3;
     session_register ("num");
   }


 ?>
The number is : <? echo $num ?> <p>

Click <a href = " " >here</a> to add 1 to the number.

<?
   if ($message){
     $num+=1;
   } else {
     $message = "This is my program";
     $num = -3;
   }


 ?>
The number is : <? echo $num ?> <p>
Click <a href = "?num=<?=$num ?>&message=<?= $message?> " >here</a> to add 1 to the number.

#!/usr/bin/perl

use CGI;
$q = new CGI;
$message=$q->param('message');
$num=$q->param('num');

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

   if ($message){
     $num+=1;
   } else {
     $message = "This is my program";
     $num = -3;
   }

print qq {

The number is :  $num <p>
Click <a href = "?num=$num&message=$message " >here</a> to add 1 to the
number.
};
print $q->end_html;