Message box how to?

Nothing complex

private void yourActionCalled_MouseUp(object sender, MouseEventArgs e)
{
     DialogResult result =
         MessageBox.Show("Are you sure you want to close?",
         "Close Application?",
         MessageBoxButtons.YesNo, MessageBoxIcon.Question, 0, 0);
     switch (result)
     {
         case DialogResult.Yes:
             someAction();                   
             break;
     }
}

how to show messagebox in asp.net with c#

Can you not see the above post ? The answer is there!

That's not right. You can't use WinForms code to do that in ASP.NET . There isn't a DialogBox control.

It's a little more complicated than that. The way I normally make a modal dialog box is to use the Modal Popup control in the AJAX.NET toolkit. You can build a panel, lay it out to look like a MessageBox, and then at the right time call an event to pop it up.

That's one way of approaching it. If you just want to pop up an informational Messagebox with little interaction, you could try using a JavaScript function or something.

Just for funn have look here