C#

public partial class Form1 : Form
{

  private Thread comReadThread;
  private Boolean comReadThreadRunning;
  private SerialPort comPort;
  delegate void SetTextCallback(string text);

  public Form1()
  {
    comReadThread = new Thread(new ThreadStart(this.comReadThreadProc));
    comReadThreadRunning = true;
    comPort = new SerialPort();

    InitializeComponent();

    comPort.PortName = "COM1";
    comPort.ReadTimeout = 500;
    comPort.WriteTimeout = 500;
    comPort.BaudRate = 9600;
    comPort.Open();

    InitializeThreads();
  }

  private void InitializeThreads()
  {
    comReadThread.Start();
  }

  private void comReadThreadProc()
  {
    byte readByte;
    StringBuilder readLine = new StringBuilder();

    while (this.comReadThreadRunning)
    {
      try
      {
        readByte = (byte)this.comPort.ReadByte();
        if (readByte != '\r')
        {
          readLine.Append((char)readByte);
        }
        else
        {
          /* assign values to gui elements */
          String readString = readLine.ToString();
          String[] splitStrings = readString.Split(new string[] {"°C"}, 5,StringSplitOptions.None);

          if (splitStrings.Length > 0)
            this.SetText(splitStrings[0]);

          /* empty string */
          readLine = new StringBuilder();
        }
      }
      catch (TimeoutException)
      {
        /* do nothing by default on event of a timeout exception */
      }
    }
  }

  private void SetText(string text)
  {
    // InvokeRequired required compares the thread ID of the
    // calling thread to the thread ID of the creating thread.
    // If these threads are different, it returns true.
    if (this.currentTempLabel.InvokeRequired)
    {
      SetTextCallback d = new SetTextCallback(SetText);
      this.currentTempLabel.Invoke(d, new object[] { text });
      Thread.Sleep(10);
    }
    else
    {
      this.currentTempLabel.Text = text;
    }
  }

  private void button1_Click(object sender, EventArgs e)
  {
    comReadThreadRunning = false;
  }

  private void Form1_FormClosing(object sender, FormClosingEventArgs e)
  {
    comReadThreadRunning = false;
    comReadThread.Join();
  }
}