In this Post You Add Shopping Card in Asp.net

Show Number of Items Coding
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 DataTable dt = new DataTable();
        dt = (DataTable)Session["buyitems"];
        if(dt!=null)
        {

            Label8.Text = dt.Rows.Count.ToString();
        }
        else
        {
            Label8.Text = "0";
        }

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DataList ItemCommand Event Coding
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if(e.CommandName=="addtocart")
        {
            Response.Redirect("AddtoCart.aspx?id=" + e.CommandArgument.ToString());

        }


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AddToCart Page Load Coding
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 if (!IsPostBack)
        {
            DataTable dt = new DataTable();
            DataRow dr;
            dt.Columns.Add("sno");
            dt.Columns.Add("productid");
            dt.Columns.Add("productname");
            dt.Columns.Add("price");
            dt.Columns.Add("productimage");
           
            

            if (Request.QueryString["id"] != null)
            {
                if (Session["Buyitems"] == null)
                {

                    dr = dt.NewRow();
                    String mycon = "Data Source=sk-pc;Initial Catalog=Shopping;Integrated Security=True";
                    SqlConnection scon = new SqlConnection(mycon);
                    String myquery = "select * from productdetail where productid=" + Request.QueryString["id"];
                    SqlCommand cmd = new SqlCommand();
                    cmd.CommandText = myquery;
                    cmd.Connection = scon;
                    SqlDataAdapter da = new SqlDataAdapter();
                    da.SelectCommand = cmd;
                    DataSet ds = new DataSet();
                    da.Fill(ds);
                    dr["sno"] = 1;
                    dr["productid"] = ds.Tables[0].Rows[0]["productid"].ToString();
                    dr["productname"] = ds.Tables[0].Rows[0]["productname"].ToString();
                    dr["productimage"] = ds.Tables[0].Rows[0]["productimage"].ToString();
                    dr["price"] = ds.Tables[0].Rows[0]["price"].ToString();
                    dt.Rows.Add(dr);
                    GridView1.DataSource = dt;
                    GridView1.DataBind();
                    Session["buyitems"] = dt;
                }
                else
                {

                    dt = (DataTable)Session["buyitems"];
                    int sr;
                    sr = dt.Rows.Count;

                    dr = dt.NewRow();
                    String mycon = "Data Source=sk-pc;Initial Catalog=Shopping;Integrated Security=True";
                    SqlConnection scon = new SqlConnection(mycon);
                    String myquery = "select * from productdetail where productid=" + Request.QueryString["id"];
                    SqlCommand cmd = new SqlCommand();
                    cmd.CommandText = myquery;
                    cmd.Connection = scon;
                    SqlDataAdapter da = new SqlDataAdapter();
                    da.SelectCommand = cmd;
                    DataSet ds = new DataSet();
                    da.Fill(ds);
                    dr["sno"] = sr + 1;
                    dr["productid"] = ds.Tables[0].Rows[0]["productid"].ToString();
                    dr["productname"] = ds.Tables[0].Rows[0]["productname"].ToString();
                    dr["productimage"] = ds.Tables[0].Rows[0]["productimage"].ToString();
                    dr["price"] = ds.Tables[0].Rows[0]["price"].ToString();
                    dt.Rows.Add(dr);
                    GridView1.DataSource = dt;
                    GridView1.DataBind();
                    Session["buyitems"] = dt;

                }
            }
            else
            {
                dt = (DataTable)Session["buyitems"];
                GridView1.DataSource = dt;
                GridView1.DataBind(); 
            }
        }