TextWriter tsw = new StreamWriter("ping.txt");
            StreamReader tr = File.OpenText("sites.txt");
            string input = null;
            while ((input = tr.ReadLine()) != null)
            {
                string howtogeek = input;
                IPAddress addresslist = Dns.GetHostAddresses(howtogeek);
                foreach (IPAddress theaddress in addresslist)
                {
                    tsw.WriteLine(theaddress.ToString());
                }
                input = "";
                addresslist = null;
            }