how to check the status of login whether it is logged in or

bool IsLoggedIn = ((System.Web.HttpContext.Current.User != null) && 
System.Web.HttpContext.Current.User.Identity.IsAuthenticated)
 
//To allow the logged in user to access the home page of the web application after logged in.
 
    if(IsLoggedIn){//Redirect to Default pageResponse.Redirect("default.aspx");}