get alerts fron .cs file in asp.net

 put this class in app_code folder save with the name Alert.cs

using System.Web;
using System.Text;
using System.Web.UI;

/// <summary>
/// A JavaScript alert
/// </summary>
public static class Alert
{

  /// <summary>
  /// Shows a client-side JavaScript alert in the browser.
  /// </summary>
  /// <param name="message">The message to appear in the alert.</param>
  public static void Show(string message)
  {
    // Cleans the message to allow single quotation marks
    string cleanMessage = message.Replace("'", "\\'");
    string script = "<script type=\"text/javascript\">alert('" + cleanMessage + "');</script>";

    // Gets the executing web page
    Page page = HttpContext.Current.CurrentHandler as Page;

    // Checks if the handler is a Page and that the script isn't allready on the Page
    if (page != null && !page.ClientScript.IsClientScriptBlockRegistered("alert"))
    {
      page.ClientScript.RegisterClientScriptBlock(typeof(Alert), "alert", script);
    }
  }
   
}