Hi, I have a problem I do not find resolve the matter simply, when the user chooses the item from the list add value to the textbox
When I want to cancel the selection subtract the value of the textbox,
When the selection was canceled I want to know the item that was nullified CheckBoxList.SelectedValue use but do not work


Code:
       if (CheckBoxList.SelectedIndex > -1)   
      {   
         Response.Write("Checked");
         cnn.Open();
         string cmdString = "select * from [merit] where [System_Name] = '" + DropDownList5.SelectedValue + "' and [Merit] = '" + CheckBoxList.SelectedValue + "'";
         SqlCommand cmd = new SqlCommand(cmdString, cnn);
         SqlDataReader dr1 = cmd.ExecuteReader();
         while (dr1.Read())
         {
             int A;
             int B;
             int Z;
             A = Convert.ToInt32(TextBox1.Text);
             B = dr1.GetInt32(3);
             Z = A + B;
             TextBox1.Text = Z.ToString();
         }
         cnn.Close();
      }   

      else  

      {   
                   cnn.Open();
         string cmdString = "select * from [merit] where [System_Name] = '" + DropDownList5.SelectedValue + "' and [Merit] = '" + CheckBoxList.SelectedValue + "'";
         SqlCommand cmd = new SqlCommand(cmdString, cnn);
         SqlDataReader dr1 = cmd.ExecuteReader();
         while (dr1.Read())
         {
             int A;
             int B;
             int Z;
             A = Convert.ToInt32(TextBox1.Text);
             B = dr1.GetInt32(3);
             Z = A - B;
             TextBox1.Text = Z.ToString();
         }
         cnn.Close();
           
       }

thanks in advane
with my regards