public string eseguiSqlQuery(string nome,string user, string pas,string mail) {
            string ee = null;
            OleDbConnection conn = new OleDbConnection();
            conn.ConnectionString = "Provider=Microsoft.Jet.OLEDB.4.0; Data source= appuntamenti.mdb";
            try {
                conn.Open();
                string sql = "INSERT INTO utenti(nome,username,password,email) VALUES('" + nome + "','" + user + "','" + pas + "','" + mail + "');";
                OleDbCommand cmd = new OleDbCommand(sql, conn);
                OleDbDataReader dr = cmd.ExecuteReader();
            } catch(Exception ex) {
                ee = Convert.ToString(ex);
            }
            finally {
                conn.Close();
            }
            return ee;
        }   // end eseguiSqlQuery