Probleem met variabelen

 <?php
ini_set('display_errors', 1); // 0 = uit, 1 = aan
error_reporting(E_ALL);

$aCats = array('hcat', 'scat', 'mcat');

for($catteller=1; $catteller<=3; $catteller++)
{
    $soort = $aCats[$catteller - 1];
    $querytest = "SELECT id, naam FROM categorie WHERE cat = '" . $catteller . "'";
    $resulttest = mysql_query($querytest);
    
    while($row = mysql_fetch_assoc($resulttest))
    {
        $link = 'zoek.php';
        $sign = '?soort=' . $soort . '&';
        foreach($aCats AS $id => $sCat)
        {
            $aSelectedCats = (isset($_GET[$sCat])) ? explode(",", $_GET[$sCat]) : array();
            $aSelectedCats = (($id === array_search($soort, $aCats)) and (count($aSelectedCats) === 0)) ? array($row['id']) : $aSelectedCats;
            if(isset($_GET['soort']) and ($_GET['soort'] === $soort))
            {
                if(in_array($row['id'], $aSelectedCats))
                {
                    unset($aSelectedCats[array_search($row['id'], $aSelectedCats)]);
                }
                elseif($_GET['soort'] === $sCat)
                {
                    $aSelectedCats[] = $row['id'];
                }
            }
            if(count($aSelectedCats) > 0)
            {
                $link .= $sign . $sCat . '=' . implode(",", $aSelectedCats);
                $sign = '&';
            }
        }
        echo '<a href="' . $link . '">' . $row['naam'] . '</a><br />';
    }
    echo '<br /><br />';
}
?>  

<?php
ini_set('display_errors', 1); // 0 = uit, 1 = aan
error_reporting(E_ALL);
 
$aCats = array('hcat', 'scat', 'mcat');
 
for($catteller=1; $catteller<=3; $catteller++)
{
    $soort = $aCats[$catteller - 1];
    $querytest = "SELECT id, naam FROM categorie WHERE cat = '" . $catteller . "'";
    $resulttest = mysql_query($querytest);
 
    while($row = mysql_fetch_assoc($resulttest))
    {
        $link = 'zoek.php';
        $sign = '?soort=' . $soort . '&';
        foreach($aCats AS $id => $sCat)
        {
            $aSelectedCats = (isset($_GET[$sCat])) ? explode(",", $_GET[$sCat]) : array();
            $aSelectedCats = (($id === array_search($soort, $aCats)) and (count($aSelectedCats) === 0)) ? array($row['id']) : $aSelectedCats;
            if(isset($_GET['soort']) and ($_GET['soort'] === $soort))
            {
                if(in_array($row['id'], $aSelectedCats))
                {
                    unset($aSelectedCats[array_search($row['id'], $aSelectedCats)]);
                }
                elseif($_GET['soort'] === $sCat)
                {
                    $aSelectedCats[] = $row['id'];
                }
            }
            if(count($aSelectedCats) > 0)
            {
                $link .= $sign . $sCat . '=' . implode(",", $aSelectedCats);
                $sign = '&';
            }
        }
        echo '<a href="' . $link . '">' . $row['naam'] . '</a><br />';
    }
    echo '<br /><br />';
}
?>

if(isset($_GET['hcat'])) { die('ja'); } else { die('nee'); }

if(isset($_GET['hcat'])) { die('ja'); } else { die('nee'); }