How to subtract and update stocks table when an order has been made

private void updateStock()
         {
            int newAmount = 0;
             try
             {
                SetConnection();
                sql_con.Open();
                sql_cmd = sql_con.CreateCommand();
                
                string CommandText = "SELECT total_in_stock FROM Stocks_record WHERE item_code = " + txtProCode.Text;
                DB5 = new SQLiteDataAdapter(CommandText, sql_con);
                //DS5.Reset();

                try
                {
                    DB5.Fill(DT5);
                    foreach (DataRow row in DT5.Rows)
                    {
                        newAmount = int.Parse(row["total_in_stock"].ToString()) - int.Parse(txtQuantity.Text);
                    }
                }
                catch (Exception e)
                {
                    MessageBox.Show("Block 1: " + e.Message);
                }

                string query = "UPDATE Stocks_record SET total_in_stock = @i WHERE item_code = " + txtProCode.Text;
                SQLiteCommand cmd = new SQLiteCommand(query, sql_con);
                cmd.CommandType = CommandType.Text;
                cmd.Parameters.AddWithValue("@i", newAmount);
                cmd.ExecuteNonQuery();
                DB5 = new SQLiteDataAdapter(CommandText, sql_con);
                DB5.Fill(DT5);

                //DT5 = DS5.Tables[0];
                dataGridView2.Refresh();
                dataGridView2.DataSource = DT5;
                sql_con.Close();
            }

             catch (Exception ex)
             {
                 MessageBox.Show(ex.Message);
             }
         }