public void addUser(User user)
        {
            string sql = "insert into Users(UserName, UserPwd) values(@name, @password)";
            SqlCommand command = Database.GetInstance().GetCommand(connection, sql);
            command.Parameters.Add("@name", SqlDbType.VarChar);
            command.Parameters.Add("@password", SqlDbType.VarChar);
            command.Parameters[0].Value = user.Username;
            command.Parameters[1].Value = user.Password;
            try
            {
                command.ExecuteNonQuery();
            }
            catch (System.Exception ex)
            {
                throw ex;
            }
            finally
            {
                Database.GetInstance().Close(command);
            }
        }