PHP HELP :::x

Bonjour, a tous j'ai un problem j crier un forum php et j'ai un error :


Notice: Undefined index: tid in C:\Program Files\EasyPHP-5.3.8.0\www\mysite\pages\view_topic.php on line 36

This Topic does not exist.

====================
mais je suis deja crier topic ;s

le code php:

=====================

<?php
include_once("config.php");
$cid = $_GET['cid'];
$tid = $_GET['tid'];
$sql = "SELECT * FROM topics WHERE category_id='".$cid."' AND id='".$tid."' LIMIT 1";
$res = mysql_query($sql) or die(mysql_error());
if (mysql_num_rows($res) == 1){
echo "<table width='100%'>";
if($_SESSION['uid']){ echo "<tr><td colspan='2'><input type='submit' value='Add reply' onClick=\"window.location = 'post_reply.php?cid=".$cid."$tid=".$tid."'\"/><br / >";
while ($row = mysql_fetch_assoc($res)){
$sql2 = "SELECT * FROM posts WHERE category_id='".$cid."' AND topic_id='".$tid."'";
$res2 = mysql_query($sql2) or die(mysql_error());
while ($row2 = mysql_fetch_assoc($res2)){
echo "<tr><td valign='top' style='border: 1px solid #000000;'><div style='min-hight: 125px'>".$row['topic_title']."<br/> by ".$row2['post_creator']." - ".$row2['post_date']."<hr />".$row2['post_content']."</div></td><td width='200' valign='top' align='center' style='border: 1px solid #000000;'>User info Here</td></tr><tr><td colspan='2'><hr/></td></tr>";
}
$old_views = $row['topic_views'];
$new_views = $old_views + 1;
$sql3 = "UPDATE topics SET topic_views='".$new_views."' WHERE category_id='".$cid."' AND id='".$tid."' LIMIT 1";
$res3 = mysql_query($sql3) or die(mysql_error());
echo "</table>";
}
}else
echo "<tr><td colspan='2'><p>Please Log for enter your reply</p><hr/></td></tr>";
}else{
echo "<p> This Topic does not exist.</p>";
}
?>

========================





Merci d'avance de votre réponse !
Witek.