$objCartSession = new SC_CartSession();
$prd_type_count = count($objCartSession->cartSession);
$prd_type_arr = array_keys($objCartSession->cartSession);
if ($prd_type_count == 0) {
    $quantity = 0;
} else {
    for ($i = 0; $i < $prd_type_count; $i++) {
        $quantity += $objCartSession->getTotalQuantity($prd_type_arr[$i]);
    }
}
$this->quantity = $quantity;