using System.Net;
public bool CheckUrlVisit(string url) 
{
  try
  {
   HttpWebRequest req = (HttpWebRequest)WebRequest.Create(url);
   HttpWebResponse resp = (HttpWebResponse)req.GetResponse();
   if (resp.StatusCode == HttpStatusCode.OK)
   {
    resp.Close(); 
    return true;
   }
  }
  catch (WebException webex)
  {
   return false;
  }
  return false;
}
string[] links = { "http://www.baidu.com", "http://www.google.com", "http://www.chinabuffetflora.com" };
foreach (string link in links)
{
 HttpContext.Current.Response.Write( link+" : "+CheckUrlVisit(link)+" <br>");
}