C#

public partial class Form1 : Form
 {
     Timer timer = new Timer();
     Graphics g;
     int x2 = 100;   // the end  location of the line being drawn
     int y2 = 100;   // the end  location of the line being drawn

     public Form1()
     {
         InitializeComponent();

         timer.Tick += new EventHandler(timer_tick);
         timer.Interval = 1000;      // update graphics every sec!!
         timer.Enabled = true;
         timer.Start();

     }

     void timer_tick(object sender, EventArgs e)
     {
         //MessageBox.Show("Tick");                    // Alert the user
     }

     private void Form1_Paint(object sender, PaintEventArgs e)
     {
     }

     protected override void OnPaint(PaintEventArgs pe)
     {
         g = pe.Graphics;

         // Draw coordinate system
         Pen pn = new Pen(Color.Black, 1);
         Point pt1 = new Point(0, 0);
         Point pt2 = new Point(x2, y2++);
         g.DrawLine(pn, pt1, pt2);

         if (y2 > 300)
             y2 = 100;       // increment y-coordinate to see that onPaint gets called from timer

     }