private void btnClient_Click(object sender, EventArgs e)
        {
            int      refclient = Convert.ToInt32(cboRefClient.Text);
            clsAgent agent     = new clsAgent();

            agent      = admin.Searched_Agent_with_RefClient(refclient);
            agent_list = new List <clsAgent>();
            agent_list.Add(agent);
            if (agent.RefAgent != 0)
            {
                gridAll.DataSource = agent_list;
            }
            else
            {
                MessageBox.Show("There is no result for given condition.", "NO RESULT");
            }
        }