function demandsession()
{
session_start();
$sid=session_id();
$query_sidt="SELECT id FROM users WHERE sid='$sid'";
$result_sid=mysql_query($query_sid);
if(mysql_num_rows($result_sid)):
... blah blah
return $id; // user id
else:
return 0; // user didn't login
endif;
}


$userid=demandsession();

posle v zavisimost ot tova dali $userid e neshto si ili 0 se includvat razlichni parcheta v samia file.

puffff