How to display the messagebox if Qty "Stock It Out" c #

Question

this my database Sql Server mines Qty

 

 

 

this my code C#

 

private void btn_proses_Click(object sender, EventArgs e)
        {
            conn = Koneksi.Conn;
            try
            {
                conn.Open();
                cmd = new SqlCommand("INSERT INTO Tb_Transaksi VALUES ('" + txt_KodeTransaksi.Text + "', '" + cm_pilihBarang.SelectedItem.ToString() + "', '" + txt_jumlah.Text + "', '" + Datepicker1.Value.Date.ToString("M/d/yyyy") + "', '" + cm_select.SelectedItem.ToString() + "', '" + txt_mengetahui.Text + "', '" + txt_diketahui.Text + "', '" + txt_keterangan.Text + "', '" + cm_status.SelectedItem.ToString() + "' )", conn);
                cmd.ExecuteNonQuery();

                if (cm_status.SelectedItem.ToString() == "Keluar")
                {
                    cmd = new SqlCommand("UPDATE Tb_Barang SET Qty=Qty - '"+txt_jumlah.Text +"' WHERE Nama_Barang= '"+ cm_pilihBarang.SelectedItem.ToString() +"'", conn);
                    cmd.ExecuteNonQuery();
                }

                if (cm_status.SelectedItem.ToString() == "Masuk")
                {
                    cmd = new SqlCommand("UPDATE Tb_Barang SET Qty=Qty + '" + txt_jumlah.Text + "' WHERE Nama_Barang= '" + cm_pilihBarang.SelectedItem.ToString() + "'", conn);
                    cmd.ExecuteNonQuery();
                }
                MessageBox.Show("Data Telah Masuk");

            }
            catch (Exception ex)
            {
                MessageBox.Show("Erorr", ex.Message);
            }
            finally
            {
                autokode_transaksi();
                conn.Close();
                Datagrid_Transaksi();
            }
        }