上网下载了一个购物车，可以用了，但我想那些被放进购物篮的产品按他们的编号排序，怎样怎样改，才行，以下是我下载的购物车的代码：
[php]
class Basket {
var $basket_count;
var $basket_item_id;
var $basket_item_name;
var $basket_item_quantity;
var $basket_item_data;
var $basket_item_price;
var $basket_item_tax;
var $basket_item_color;
var $basket_item_size;

function Basket() {
$this->basket_count=0;
}
function Add_Item($ID,$name,$quantity=1,$price=0,$data='',$tax,$color,$size,$weight) {

$this->basket_item_id[$this->basket_count]=$ID;//ÉÌÆ·ID
$this->basket_item_name[$this->basket_count]=$name;//ÉÌÆ·Ãû³Æ
$this->basket_item_quantity[$this->basket_count]=$quantity;//ÉÌÆ·ÊýÁ¿
$this->basket_item_data[$this->basket_count]=$data;//ÈÕÆÚ
$this->basket_item_price[$this->basket_count]=$price;//¼Û¸ñ
$this->basket_item_tax[$this->basket_count]=$tax;
$this->basket_item_color[$this->basket_count]=$color;
$this->basket_item_size[$this->basket_count]=$size;
$this->basket_item_weight[$this->basket_count]=$weight;

$this->basket_count++;
return ($this->basket_count-1);
}
function Del_Item($pos) {
$this->basket_item_id[$pos]='';
}
function Get_Item_ID($pos) {
return $this->basket_item_id[$pos];
}
function Get_Item_Name($pos) {
return $this->basket_item_name[$pos];
}
function Get_Item_Price($pos) {
return $this->basket_item_price[$pos];
}
function Get_Item_Quantity($pos) {
return $this->basket_item_quantity[$pos];
}
function Get_Item_Data($pos) {
return $this->basket_item_data[$pos];
}
function Get_Item_Tax($pos) {
return $this->basket_item_tax[$pos];
}
function Get_Item_Color($pos) {
return $this->basket_item_color[$pos];
}
function Get_Item_Size($pos) {
return $this->basket_item_size[$pos];
}
function Get_Item_Weight($pos) {
return $this->basket_item_weight[$pos];
}
function Set_Item_Quantity($pos,$quantity) {
$this->basket_item_quantity[$pos]=$quantity;
}
function Set_Item_Data($pos,$data) {
$this->basket_item_data[$pos]=$data;
}
function Enum_Items($start=false) {
static $current;
if ($current>=$this->basket_count) return -1;
if (!$start) {
$current++;
} else {
$current=0;
}
while (($this->basket_item_id[$current]=='') && ($current<$this->basket_count)) {
$current++;
}
return ($current<$this->basket_count) ? $current : -1;
}
function Empty_Basket() {
$this->basket_count=0;
}
function Get_Basket_Count() {
$num=0;
for ($i=0;$i<$this->basket_count;$i++) {
if ($this->basket_item_id[$i]!='') $num++;
}
return $num;
}
}
[/php]