title: check URL exists or throws page not found message in asp.net
body: <p>I want to validate an url, whether it exists or throwing page not found error. can anyone help me how to do it in asp.net.
  for e.g., my url may be like <code>http://www.stackoverflow.com</code> or <code>www.google.com</code> i.e., it may contain <code>http://</code> or may not. when i check, it should return the webpage valid if exists or page not found if doesnot exists</p>
  
  <p>i tried <code>HttpWebRequest</code> method but it needs "<code>http://</code>" in the url.</p>
  
  <p>thanks in advance.</p>