private void b_lookfor_Click(object sender, EventArgs e)
        {
            string sql_str = "";
            DataTable dt1 = new DataTable();
            DataTable dt2 = new DataTable();
            fee_conn fee_conn = new fee_conn();
            SqlDataAdapter find_do;
            if (DateTime.Compare(d_end, d_start) > 0)
            {
                
                SqlConnection conn = new SqlConnection(fee_conn.sql_conn());
                sql_str = "select * from car_park_fee where car_fee_flag = 1";
                find_do = new SqlDataAdapter(sql_str, conn);
                find_do.Fill(dt1);

                sql_str = "select * from car_park_fee where car_fee_flag = 2";
                find_do = new SqlDataAdapter(sql_str, conn);
                find_do.Fill(dt2);

                dt1.Merge(dt2);
                d_report.Visible = true;
                d_report.DataSource = dt1;
       
                            
             }   
    }