C#

using System;
using System.Windows.Forms;
using System.IO.Ports;

namespace serialport
{
public partial class Form1 : Form
{
private SerialPort port = new SerialPort("COM3", 9600, Parity.Odd, 8, StopBits.One);

public Form1()
{
InitializeComponent(); port.Open();
}


private void buttonSS_Click(object sender, EventArgs e)
{
timer1.Enabled = !timer1.Enabled; //on/off event
}



private void timer1_Tick(object sender, EventArgs e)
{
port.DtrEnable = !port.DtrEnable;

if (port.DtrEnable)
{
timer1.Interval = (int)numericUpDown1.Value;//1 val
}
else
{
timer1.Interval = (int)numericUpDown2.Value;//2 val
}
}

OrderInfo customerChoices = new OrderInfo();

#region Appetizer ComboBox
        private void cmboBoxAppetizer_SelectedIndexChanged(object sender, EventArgs e)
        {
            switch (cmboBoxAppetizer.SelectedIndex)
            {
                case 0:
                    {

                        frmQuantity frmQuantity = new frmQuantity();
                        frmQuantity.Show();

                        customerChoices.Appetizer = cmboBoxAppetizer.Text;
                        label1.Text = customerChoices.Quantity
                    }
                    break;
                case 1:
                    {
                        frmQuantity frmQuantity = new frmQuantity();
                        frmQuantity.Show();
                    }
                    break;
                case 2:
                    {
                        frmQuantity frmQuantity = new frmQuantity();
                        frmQuantity.Show();
                    }
                    break;
                default:
                    {
                    }
                    break;
            }
        }
        #endregion 

public partial class frmQuantity : Form
    {
        OrderInfo customerChoices = new OrderInfo();

        public frmQuantity()
        {
            InitializeComponent();
        }

        private void txtBoxQuantity_TextChanged(object sender, EventArgs e)
        {
            txtBoxQuantity.MaxLength = Convert.ToInt32(txtBoxQuantity.Text);
        }

        private void btnOk_Click(object sender, EventArgs e)
        {
            customerChoices.Quantity = Convert.ToInt32(txtBoxQuantity.Text);
            
            this.Close();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            this.Close();
        }
    }

class OrderInfo
    {

        int quantity;

        public int Quantity
        {
            get
            {
                return quantity;
            }
            set
            {
                quantity = value;
            }
        }

    }