on/off arduino

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.IO.Ports;

namespace ON_OFF_arduino
{
    public partial class Form1 : Form
    {
        public SerialPort myport;
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            myport = new SerialPort();
            myport.BaudRate = 9600;
            myport.PortName = "COM5";
            myport.Open();
            myport.WriteLine("O");
            myport.Close();
        }

        private void button2_Click(object sender, EventArgs e)
        {
            myport = new SerialPort();
            myport.BaudRate = 9600;
            myport.PortName = "COM5";
            myport.Open();
            myport.WriteLine("F");
            myport.Close();
        }
    }
}

--------------------------------------------------------------------------
void setup()
{

  Serial.begin(9600);
  pinMode(13, OUTPUT);
}



void loop()
{
  if(Serial.available())
  {
 char  data=Serial.read();
  Serial.println(data);
  switch(data)
  {
    case 'O':digitalWrite(13, HIGH);
    break;
    case 'F':digitalWrite(13, LOW);
    break;

  }
  }
}