this code will return you current ldap user or ldap users with groups

 // get current ad user
_username = System.Security.Principal. WindowsIdentity.GetCurrent().Name
                    .Split( new string [] {"\\"}, StringSplitOptions.None)[1];

     
// get all users with groups

        Dictionary<string ,string[]> userGroups;
        private void uxBtnGetir_Click(object sender, EventArgs e)
        {
            IEnumerable<User > users = GetADUsers(string.IsNullOrEmpty(uxUsername.Text));

            uxLvKullanicilar.Items.Clear();
            foreach (User _user in users)
            {
                uxLvKullanicilar.Items.Add(
                    new Infragistics.Win.UltraWinListView.UltraListViewItem (
                        _user.sAMAccountName, new object [] { _user.Name, _user.mail }));

                userGroups.Add(_user.sAMAccountName, _user.Groups);
            }
        }


        static DirectoryEntry ROOT = new DirectoryEntry("LDAP://Company" );
        private static string username;

        private static IEnumerable< User> GetADUsers(bool allusers=false)
        {
            IEnumerable<User > users;

            var usersDS = new DirectorySource< User>(ROOT, SearchScope .Subtree);
            string usernameq = allusers ? "*" : "*"   username   "*";
            users = from usr in usersDS
                    where usr.Name == usernameq
                    select usr;

            users = users.OrderBy(user => user.Name).ToList();

            return users;
        }