Add user in SP site Programatically

SPSite thisSite1 = SPControl.GetContextSite(HttpContext.Current);
SPWeb web = thisSite1.OpenWeb();
web.AllowUnsafeUpdates = true;
web.SiteUsers.Add("bomcordom:" + _userid, "", _userid, "");
web.Groups[].AddUser("bomcordom:" + _userid, "", _userid, "");