changing session variables

[Anon]

When I set the variable gquery in this function
<?
session_start();

session_register("gquery");

function showquery() {
?>
<CENTER>
<FORM ACTION="<?=$PHP_SELF?>" METHOD="Post">
Search:<INPUT TYPE=text NAME=gquery VALUE="<?echo $gquery ?>">
<INPUT TYPE="submit" VALUE="search">
</FORM></CENTER>
<?
}

In the code fragment:

if(!isset($gquery)) {
showquery();
}else
{

         showquery();
         echo "gquery=$gquery<BR>";
}

Once show query is called the value of $gquery should be overwritten but instead, $gquery stays the same until I unset the session variable? can a session variable only be written to once? Is the the wrong way to handle a persistent variable?
I have even tried passing the variable to the function showquery and getting gquery from a returned local variable, but that returns nothing each time.

[mkarabulut]

according to the PHP session mentality, if you have registered a variable , the registered value doesn't change simultaneously if the variable's value is changed in the script. You should re-register the value manually into the session.
check it .
<?
$value="Mustafa";
session_register('value');
$value="Karabulut";
echo $HTTP_SESSION_VARS["value"];
//it will print Mustafa

session_register('value');
echo $HTTP_SESSION_VARS["value"];
//it will print Karabulut

?>

[Anon]

if I do that then it seems like I should adjust my form function to be:
<?
function showquery() {
?>
<CENTER>
<FORM ACTION="<?=$PHP_SELF?>" METHOD="Post">
Search:<INPUT TYPE=text NAME=gquery VALUE="<? echo $gquery?>">
<INPUT TYPE="submit" VALUE="search">
</FORM></CENTER>
<?
session_register('gquery');
}

but this still only gives me the first entry into gquery, if I access the function again, I always get the first value for gquery? it seems like I am going about this the wrong way?