Page_Load method in Default.asp.cs

gistfile1.cs

private void Page_Load(object sender, System.EventArgs e)
{
  if (!this.IsPostBack)

    // Create a random code and store it in the Session object.
    this.Session["CaptchaImageText"] = GenerateRandomCode();

  else
  {
    // On a postback, check the user input.
    if (this.CodeNumberTextBox.Text == this.Session["CaptchaImageText"].ToString())
    {
      // Display an informational message.
      this.MessageLabel.CssClass = "info";
      this.MessageLabel.Text = "Correct!";
    }
    else
    {
      // Display an error message.
      this.MessageLabel.CssClass = "error";
      this.MessageLabel.Text = "ERROR: Incorrect, try again.";

      // Clear the input and create a new random code.
      this.CodeNumberTextBox.Text = "";
      this.Session["CaptchaImageText"] = GenerateRandomCode();
    }
  }
}