A relatively complete shopping cart class implemented in PHP, php shopping cart class_PHP tutorial

/*****************************************************************************/
/*                                                                                                            /* file type: Contains files, the recommended suffix is ​​.inc /*                                                                                                              /* file name: cart.inc /*                                                                                                            /* Description: Define a car purchase category */
/*                                                                                                            /* Func list: class cart /*                                                                                                              /* author: bigeagle /*                                                                                                           /*                                                                                                              /*****************************************************************************/

//Define constants for this file
define("_CART_INC_" , "exists") ;

/*Shopping cart class*/
class TCart
{

var $SortCount; //Number of product categories
var $TotalCost; //Total value of goods

var $Id; //ID of each type of product (array)
var $Name; //The name of each type of product (array)
var $Price; //The price of each type of product (array)
var $Discount; //Product discount (array)
var $GoodPrice ; //The preferential price of the product (array)
var $Count; //The number of pieces of each type of product (array)
var $MaxCount ; //Product limit (array)

//******构造函数
  function TCart()
  {
   $this->SortCount=0;
 
   session_start(); //初始化一个session
   session_register('sId');
   session_register('sName');
   session_register('sPrice');
   session_register('sDiscount');
   session_register('sGoodPrice') ;
   session_register('sCount') ;
   session_register('sMaxCount') ;
 
   $this->Update();
   $this->Calculate();
  }
 
  //********私有，根据session的值更新类中相应数据
  function Update()
  {
    global $sId,$sName,$sPrice,$sCount,$sDiscount,$sMaxCount,$sGoodPrice;
 
   if(!isset($sId) or !isset($sName) or !isset($sPrice)
      or !isset($sDiscount) or !isset($sMaxCount)
      or !isset($sGoodPrice) or !isset($sCount)) return;
 
   $this->Id        =$sId;
   $this->Name      =$sName;
   $this->Price     =$sPrice;
   $this->Count     =$sCount;
   $this->Discount  = $sDiscount ;
   $this->GoodPrice = $sGoodPrice ;
   $this->MaxCount  = $sMaxCount ;
 
   //计算商品总数
   $this->SortCount=count($sId);
 
  }
 
  //********私有，根据新的数据计算每类商品的价值及全部商品的总价
  function Calculate()
  {
   for($i=0;$i<$this->SortCount;$i++)
   {
     /*计算每件商品的价值，如果折扣是0 ，则为优惠价格*/
$GiftPrice = ($this->Discount[$i] == 0 ? $this->GoodPrice :
                      ceil($this->Price[$i] * $this->Discount[$i])/100 );
$this->TotalCost += $GiftPrice * $this->Count[$i] ;
}
}

//**************The following are interface functions

//*** Add an item
// Determine whether there is already one in the blue, if so, add count, otherwise add a new product
//First, change the value of the session, and then call update() and calculate() to update the member variables
function Add($a_ID , $a_Name , $a_Price , $a_Discount ,
$a_GoodPrice , $a_MaxCount , $a_Count)
{
global $sId , $sName , $sCount , $sPrice , $sDiscount ,
$sGoodPrice , $sMaxCount ;

$k=count($sId);
for ($i=0; $i<$k; $i++)
{ //First check if this product has been added
If($sId[$i]==$a_ID)
{
$sCount[$i] += $a_Count ;
        break;
}  
}
if($i >= $k)
{ //If not, add a new product category
$sId[] = $a_ID;
$sName[] = $a_Name;
$sPrice[] = $a_Price;
$sCount[] = $a_Count;
$sGoodPrice[] = $a_GoodPrice;
$sDiscount[] = $a_Discount;
$sMaxCount[] = $a_MaxCount;
}

$this->Update(); //Update the member data of the class
$this->Calculate();
}

//Remove an item
function Remove($a_ID)
{
global $sId , $sName , $sCount , $sPrice , $sDiscount ,
$sGoodPrice , $sMaxCount ;

$k = count($sId);
for($i=0; $i < $k; $i++)
{
If($sId[$i] == $a_ID)
{
        $sCount[$i] = 0;
        break;
}  
}

$this->Update();
$this->Calculate();
}

//Change the number of items
function ModifyCount($a_i,$a_Count)
{
global $sCount;

$sCount[$a_i] = $a_Count ;
$this->Update();
$this->Calculate();
}

/*****************************
Clear all products
*******************************/
function RemoveAll()
{
session_unregister('sId');
Session_unregister('sName');
Session_unregister('sPrice');
Session_unregister('sDiscount');
session_unregister('sGoodPrice') ;
session_unregister('sCount') ;
Session_unregister('sMaxCount') ;
$this->SortCount = 0;
$this->TotalCost = 0;
}

//Whether a certain product is already in the blue, the parameter is the ID of this product
function Exists($a_ID)
{
for($i=0; $i<$this->SortCount; $i++)
{
If($this->Id[$i]==$a_ID) return TRUE;
}
Return FALSE;
}

//The position of a certain item in the blue
function IndexOf($a_ID)
{
for($i=0; $i<$this->SortCount; $i++)
{
If($this->Id[$i]==$id) return $i;
}
Return 0;
}

//Get information about a product, main working function
//Return an associative array,
function Item($i)
{
$Result[id] = $this->Id[$i];
$Result[name] = $this->Name[$i];
$Result[price] = $this->Price[$i];
$Result[count] = $this->Count[$i];
$Result[discount] = $this->Discount[$i] ;
$Result[goodprice] = $this->GoodPrice[$i] ;
$Result[maxcount] = $this->MaxCount[i];
Return $Result;
}

//Get the total number of product categories
function CartCount()
{
Return $this->SortCount;
}

//Get the total product value
function GetTotalCost()
{
Return $this->TotalCost;
}
}
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