C# – User permission check for a particular site in SharePoint

I need to check whether a particular user has access to a site/subsite in SharePoint programmatically.

Note: login user can have acces to few sites in my SharePoint site. So I have to show sites only to which the user have permission.

I used:

   using (SPWeb web = new SPSite(url).OpenWeb())
                {
                    SPWebCollection Sites = web.Webs;

                    foreach (SPWeb website in Sites)
                    {
                        SPUser loginUser = website.CurrentUser;
                        string username = loginUser.Name;
                        if (!website.IsRootWeb)
                        {
                            SPWebCollection subsites = website.Webs;
                            foreach (SPWeb supersubsite in subsites)
                            {

                                SPWebCollection thirdlevelsites = supersubsite.Webs;
                                foreach (SPWeb thirdlevel in thirdlevelsites)
                                {

thirdlevel.Site.CatchAccessDeniedException = false;
                                bool check = thirdlevel.DoesUserHavePermissions(SPContext.Current.Web.CurrentUser.LoginName, SPBasePermissions.Open);
                                if (check)
                                {
                                }
                                thirdlevel.Site.CatchAccessDeniedException = true;                                   
                                }

                            }
                        }
                    }
                }

but getting error at

bool check = thirdlevel.DoesUserHavePermissions(SPContext.Current.Web.CurrentUser.LoginName, SPBasePermissions.Open);

as :

Access is denied. (Exception from HRESULT: 0x80070005 (E_ACCESSDENIED))