Sign Guestbook Not Working In Xhtml

[Guest]

Why does this sign guestbook not work ? it goes through the process etc but does not update

else if($action=="signgb")
{
$who=$_GET["who"];
addonline(getuid_sid($sid),"Signing Users guestbook","");
if(!cansigngb(getuid_sid($sid), $who))
    {

      echo "<p align=\"center\">";
      echo "You cant Sign this user guestbook

";
      echo "<a href=\"index.php?action=main&amp;sid=$sid\">Home</a>";
      echo "</p>";
      exit();
    }
    

    echo "<p align=\"center\">";
echo "<form action=\"genproc.php?action=signgb&amp;sid=$sid\" method=\"post\">";
    echo "Text:<input name=\"msgtxt\" maxlength=\"500\"/>
";
echo "<input type=\"submit\" value=\"GO\"/>";
            echo "</form>";

         echo "

<a href=\"index.php?action=main&amp;sid=$sid\"><img src=\"images/home.gif\" alt=\"*\"/>";
echo "Home</a>";
    echo "</p>";
    
}


else if($action=="online")
{

  addonline(getuid_sid($sid),"Online List","");

[Guest]

Managed to fix it by adding these 2 lines :

echo "<input type=\"hidden\" name=\"who\" value=\"$who\"/>";
         echo "<input type=\"hidden\" name=\"uid\" value=\"$sid\"/>";