title: How do I display an error message in asp.net?
body: <p>I have a bunch of text boxes and a save button to update something. When I click Save I have code that determines whether they are correctly filled in, in the code behind file.</p>
  
  <p>If they are not correctly filled in, I want to display an error message in the form of an alert.</p>
  
  <p>What is the best way to do this? Pressing the button obviously makes the page postback, so I thought about adding something to the URL like <code>mypage.aspx?errormessage=blahblah</code> but I don't know if this is the best way or even how to do it...</p>
  
  <p>Any suggestions?</p>