• Rather than providing a standalone program, we could instead provide a form in HTML which causes a program to be run (when the form's button is clicked).
• Traditionally, this program is a CGI program often written in Perl.
• Or, if you have appropriate web server software (such as Apache's httpd), it could be written in PHP.
• Or, if you use tomcat, it could be written in Java (a servlet).
• And now, if you use IIS (Microsoft's web server software), the program could be written in a .NET language.
• Such a WWW page is called an ASP.NET page.

• Probably easiest to use Visual Studio.NET's wizard rather than write the code yourself.
• We can get it to generate a webform in the file WebForm1.aspx:

  <%@ ... language="c#" Codebehind="WebForm1.aspx.cs" 
                      ... Inherits="WebFormConvert.WebForm1" %>
  <form id="Form1" ... >
      <asp:TextBox id="TextBox1" ...
      </asp:TextBox>
      <asp:Button id="Button1" ...
                Text="Get Fahrenheit" ...
      </asp:Button>
      <asp:Label id="Label1" ...
      </asp:Label>
  </form>
  

• This HTML includes a directive to IIS to say that the supporting code is in C# and it is in the file WebForm1.aspx.cs.
• The directive also refers to the class WebFormConvert.WebForm1.
• And the ids TextBox1, Button1 and Label1 are references to fields of the class.

• As well as producing the webform, Visual Studio.NET automatically generates a lot of code in C# (or VB.NET).
• This code includes declarations for TextBox1, Button1 and Label1.
• The only code you need to provide yourself is the body of the Button1_Click method.
• This method gets executed whenever the user hits the Get Fahrenheit button of the form.
• When Button1_Click refers to TextBox1.Text, it is referring to whatever text the user typed into the text box of the form.
• Similarly, when Button1_Click assigns a value to Label1.Text, it is changing what appears in the label of the form.

using System;
using System.Collections;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Web;
using System.Web.SessionState;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.HtmlControls;
namespace WebFormConvert
{
    public class WebForm1 : Page
    {
        protected TextBox TextBox1;
        protected Button Button1;
        protected Label Label1;
        private void Page_Load(object sender, EventArgs e)
        {
        }
        override protected void OnInit(EventArgs e)
        {
            InitializeComponent();
            base.OnInit(e);
        }
        private void InitializeComponent()
        {    
            this.Button1.Click += new System.EventHandler(this.Button1_Click);
            this.Load += new System.EventHandler(this.Page_Load);
        }
        private void Button1_Click(object sender, EventArgs e)
        {
            double tCentigrade = double.Parse(TextBox1.Text);
            double tFahrenheit = 32 + tCentigrade*9/5;
            Label1.Text = tFahrenheit.ToString();
        }
    }
}