Use Code behind : Code behind « ASP.Net Instroduction « ASP.NET Tutorial

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="FirstPageCodeBehind" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
  "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml" >
<head id="Head1" runat="server">
    <title>First Page Code-Behind</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>

    <asp:Button
        id="Button1"
        Text="Click Here"
        OnClick="Button1_Click"
        Runat="server" />

    <br /><br />

    <asp:Label
        id="Label1"
        Runat="server" />

    </div>
    </form>
</body>
</html>


File: Default.aspx.cs

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;

public partial class FirstPageCodeBehind : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        Label1.Text = "Click the Button";
    }

    protected void Button1_Click(object sender, EventArgs e)
    {
        Label1.Text = "Thanks!";
    }
}

1.3.Code behind
	1.3.1.	code-inline model: all the code is contained within a single .aspx page
	1.3.2.	code-behind model allows for code separation of the page's business logic from its presentation logic
	1.3.3.	Use Code behind
	1.3.4.	Code behind (VB.net)