use the Paint event like this
private void form_Paint(object sender, PaintEventArgs e)
{
Random RandomClass = new Random();
int height = 1;
for (int i = 0; i < 200; i++)
{
height += 2;
int RandomNumber = RandomClass.Next(11, 111);
System.Drawing.Graphics my_graph = e.Graphics;
Point my_point_one = new System.Drawing.Point(10, 2*(i+1));
Point my_point_two = new System.Drawing.Point(RandomNumber, 2 * (i + 1));
my_graph.DrawLine(System.Drawing.Pens.Blue, my_point_one, my_point_two);
}
}