โค๊ดลักษณะนี้จะเขียนตรวจสอบเพิ่มเติมยังไงได้ครับ (รบกวนที)

<?
session_start();
if (!isset($_SESSION['CART'])){ $_SESSION['CART'] = array(); }
if (isset($_POST['txtname']) && isset($_POST['txtpricex']) && isset($_POST['txtUnit']) && isset($_POST['txtimage']) && isset($_POST['txtid'])){
	$ITEM = array(
		'id' => $_POST['txtid'],
		'name' => $_POST['txtname'],
		'priceper' => $_POST['txtpricex'], 
		'unit' => $_POST['txtUnit']	,	
		'image' => $_POST['txtimage']
		);
	$_SESSION['CART'][] =  $ITEM;
	header('Location: ' . $_SERVER['PHP_SELF']);
}
else if (isset($_GET['remove'])){
	unset($_SESSION['CART'][$_GET['remove']]);
	header('Location: ' . $_SERVER['PHP_SELF']);
}
else if (isset($_GET['empty'])){
	session_destroy();
	header('Location: ' . $_SERVER['PHP_SELF']);
}
else if (isset($_POST['update'])) {
	foreach ($_POST['items_unit'] as $itemID => $unit) {
		if ($unit == 0) {
			unset($_SESSION['CART'][$itemID]);
		}
		else if($unit >= 1) {
			$_SESSION['CART'][$itemID]['unit'] = $unit;
		}
	}
	header('Location: ' . $_SERVER['PHP_SELF']);
}
?>