Arduino interfacing cSharp

add using System.IO.Ports;
add SerialPort port = new SerialPort();

public Form1()
{
    button1.Enable = true; // Connect Button
    button2.Enable = flase; // ON button
    button3.Enable = false; // OFF Button

    InitializeComponent();
}

private void button1_Click(object sender, EventArgs e)
{
    port.BaudRate = 9600;
    port.PortName = textbox1.text;

    try
    {
        port.Open();
        // if connected
        button1.Enable = false; // Connect button disable.
        button2.Enable = true; // On Button Enable.
    } catch (Exception ex)
    {
        MessageBox.Show(ex.Message, "ERROR OCCURRED");
    }
}

private void button2_Click(object sender, EventArgs e)
{
    port.WriteLine("ON");
    button2.Enable = false;
    button3.Enable = true;
}

private void button3_Click(object sender, EventArgs e)
{
    port.WriteLine("OFF");
    button2.Enable = true;
    button3.Enable = false;
}