asp.Net学習ノート・Cookie

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

public partial class      : System.Web.UI.Page
{
    private int a = 0;
    protected void Page_Load(object sender, EventArgs e)
    {
        if (IsPostBack)
        {
            Response.SetCookie(new HttpCookie("num", "0"));
//  HttpCookie  
            this.Label1.Text = "0";
        }
    }
    protected void Button1_Click(object sender, EventArgs e)
    {
          int.TryParse(Request.Cookies["num"].Value, out a);
            a++;
            Response.SetCookie(new HttpCookie("num", a.ToString()));
            this.Label1.Text = a.ToString();
       
    }
}