Vérification du scripts php,aidez moi c urgen

Bonjour,

---------------------------------vente.php--------------------------
<form action='vente2.php' method='post' name='form'>
<?php
echo "Type de bien *:<select name='bien' size='1' >";
echo "<option name='maison'>maison </option>";
echo "<option name='appartement'>appartement </option>";
echo "<option name='fonds_commerce'>fonds commerce </option>";
echo "</select><br>";
echo "Code postal *:<input type='text' name='codep' value='' size='17'><br>";
echo "(EX:4060)- <ahref='aide.php'>aide</a><br>";
echo "<center><input type='submit' name='e1' value='Suite'></center>";
echo "</form>";
?>
</form>


---------------------------------vente2.php--------------------------

<form action='vente3.php' method='post' name='form'>
<?php
extract ($_POST,EXTR_OVERWRITE);
$id=mysql_connect("localhost","root","") or die ("serveur introuvable!!!");
$db=mysql_select_db("immobilier") or die ("base introuvable!!!");
$res=mysql_query("select distinct ville
from maisons where '$bien'='maison' and code_postal='$code' "); /*line 311*/
$res=mysql_query("select distinct ville
from appartements where '$bien'='appartement' and code_postal='$code' "); /*line 313*/
$res=mysql_query("select distinct ville
from fonds_de_commerce where '$bien'='fonds_commerce' and code_postal='$code' "); /*line 315 */

$n=mysql_num_rows($res);
echo "Selectionnez une ville <select name='ville' size='1'>";
for($i=0 ;$i<$n;$i++)
{
$data=mysql_fetch_array($res);
echo "<option value'$data[0]'>$data[0]</option>";
}
echo "</select><br>";

echo "<center><input name='s2' type='submit' value='Suite'></center>";
?>
</form>


----------------------------------------------------------------------------------------------------------------------
quand je essaier d'executer la 2éme script "vente2.php" ,il m'affiche ces erreures

""" Notice: Undefined variable: code in c:\program files\easyphp1-8\www\pfe\vente2.php on line 311

Notice: Undefined variable: code in c:\program files\easyphp1-8\www\pfe\vente2.php on line 313

Notice: Undefined variable: code in c:\program files\easyphp1-8\www\pfe\vente2.php on line 315 """


aidez moi svp c trés urgent et merci