我的购物车代码里面只能加一件商品，急！
using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Text;
using System.Data.SqlClient;

public partial class ShoppingCart : System.Web.UI.Page
{
  public int goods_id = 0;
  public int ProdCount = 0;

  public int sum = 0;
  DataSet ds = new DataSet();
  DataTable newDT = new DataTable("CartTable");
  DataColumn newDC;
  protected void Page_Load(object sender, EventArgs e)
  {
  if (!IsPostBack)
  {
  HttpCookie cookie = Request.Cookies["UserInfo"];
  if (null == cookie)
  {
  Response.Write("<script>location.href='login.aspx'</script>");
  Response.End();
  }

  if (Request.QueryString["goods_id"] != null || Request.QueryString["goods_id"] != "")
  {
  goods_id = Convert.ToInt32(Request.QueryString["goods_id"]);
  }
  if (Request.QueryString["ProdCount"] != null || Request.QueryString["ProdCount"] != "")
  {
  ProdCount = Convert.ToInt32(Request.QueryString["ProdCount"]);
  }


   
  ds.Tables.Add(newDT);
   
  newDC = new DataColumn("ProdID", System.Type.GetType("System.Int32"));
  ds.Tables["CartTable"].Columns.Add(newDC);
  newDC = new DataColumn("ProdCount", System.Type.GetType("System.Int32"));
  newDC.DefaultValue = 1;
  ds.Tables["CartTable"].Columns.Add(newDC);
  newDC = new DataColumn("ProName", System.Type.GetType("System.String"));
  ds.Tables["CartTable"].Columns.Add(newDC);
  newDC = new DataColumn("SalePrice", System.Type.GetType("System.Double"));
  ds.Tables["CartTable"].Columns.Add(newDC);
  newDC = new DataColumn("MarketPrice", System.Type.GetType("System.Double"));
  ds.Tables["CartTable"].Columns.Add(newDC);
  Session["myCartTable"] = ds;
  StringBuilder strSqlString = new StringBuilder();
  strSqlString.Append("select ");
  strSqlString.Append("pro_name, ");
  strSqlString.Append("pro_sale_price, ");
  strSqlString.Append("pro_market_price ");
  strSqlString.Append("from ");
  strSqlString.Append("tb_products ");
  strSqlString.Append("where ");
  strSqlString.Append("pro_id = " + goods_id);
  DataSet dss = SqlHelper.GetDataSet(SqlHelper.ConnectionString, CommandType.Text, strSqlString.ToString(), null);
  if (goods_id > 0)
  {
  if (dss.Tables[0].Rows.Count > 0)
  {
  DataRow dr = newDT.NewRow();
  dr[