Principle of novice shopping cart implementation in php

//加入购物车
function addcart($goods_id,$goods_num){
  
$cur_cart_array = unserialize(stripslashes($_COOKIE['shop_cart_info']));
  if($cur_cart_array==""){
  
   $cart_info[0][] = $goods_id;
   $cart_info[0][] = $goods_num;
   
   setcookie("shop_cart_info",serialize($cart_info));
   
  }elseif($cur_cart_array<>""){
   
   //返回数组键名倒序取最大
   $ar_keys = array_keys($cur_cart_array);
   rsort($ar_keys);
   $max_array_keyid = $ar_keys[0]+1;
   
   //遍历当前的购物车数组
   //遍历每个商品信息数组的0值，如果键值为0且货号相同则购物车存在相同货品
   foreach($cur_cart_array as $goods_current_cart){
    foreach($goods_current_cart as $key=>$goods_current_id){
     if($key == 0 and $goods_current_id == $goods_id){
   echo "<script language=javascript>";
   echo "if(confirm(&#39;购物车已经有该商品，继续购物按----确定!查看购物车按----取消!&#39;))";
   echo "{history.go(-1)}";
   echo "else{window.location.href=&#39;http://blog.163.com/wz_pk007/blog/xqs_cart.php&#39;}";
   echo "</script>";
      exit();
     }
    }
   }
   
   $cur_cart_array[$max_array_keyid][] = $goods_id;
   $cur_cart_array[$max_array_keyid][] = $goods_num;
   
   setcookie("shop_cart_info",serialize($cur_cart_array));
     
  }
  
}
  
//从购物车删除
function delcart($goods_array_id){
  
$cur_goods_array = unserialize(stripslashes($_COOKIE[&#39;shop_cart_info&#39;]));
  
//删除该商品在数组中的位置
  unset($cur_goods_array[$goods_array_id]);
  setcookie("shop_cart_info",serialize($cur_goods_array));
  
}
  
//修改购物车货品数量
function update_cart($up_id,$up_num,$goods_ids){
  
  //先清空cookie,以便重新设置，传递过来三个数组参数 1数组的标识 2商品数量数组 3商品编号数组
  //如果不清空cookie则无法处理数量为零的商品
  setcookie("shop_cart_info","");
  foreach($up_id as $song){
  
   //先返回数组当前单元；再把指针向下移动一个位置
   $goods_nums = current($up_num);
   $goods_id = current($goods_ids);
   next($up_num);
   next($goods_ids);
   
   //当商品数量为空的时候，注销此处的数组值并用continue 2 语句避开下面的操作，继续做foreach循环
   while($goods_nums == 0){
    unset($song);
    continue 2;
   }
   
   $cur_goods_array[$song][0] = $goods_id;
   $cur_goods_array[$song][1] = $goods_nums;
   
  }
  
  setcookie("shop_cart_info",serialize($cur_goods_array));