Collision from boundaries of form.

Question

I have made two circles of same size on windows form application and then moved them in such a way that they will never be collided and now i want circles to reflect from boundaries of Form how this could be done in a easy way.

 

private void button11_Click(object sender, EventArgs e)

{

Pen myPen = new Pen(Color.Black);

Pen mypen2 = new Pen(Color.Black);

Graphics formGraphics;

formGraphics = this.CreateGraphics();

int x=100, y=100,x1=200,y1=200;

for (int i = 2; i < 200; i++)

{

this.Refresh();

formGraphics = this.CreateGraphics();

formGraphics.DrawEllipse(myPen, new Rectangle(x + i, y/ i, 100, 100));

formGraphics.DrawEllipse(myPen, new Rectangle(x1 / i, y1 + i, 100, 100));

System.Threading.Thread.Sleep(22);

}