static string fname = string.empty

     private static void xmlparser6(string xmldata)
            {
                XDocument xml = XDocument.Parse(xmldata);

                var q = from b in xml.Descendants("client")
                        select new
                        {
                            fname = b.Element("firstname").Value,
                            lname = b.Element("lastname").Value,
                            email = b.Element("email").Value,
                        };

                if (fname != "")
                {
                    MessageBox.Show(fname);
                }

            }

    // XML
    <?xml version="1.0" encoding="iso-8859-7"?>
    <whmcsapi version="5.1.2">
    <client>
      <userid>1</userid>
      <id>1</id>
      <firstname>john</firstname>
      <lastname>deer</lastname>
      <companyname>that one company</companyname>
      <email>noemail@email.com</email>
    </client>
    </whmcsapi>