event paint picture box

Hi: 

I have declared the variable as public pint and modify in this event: 

         private void PictureBox1_Click (object sender, EventArgs e) 

but then when I consult in the event down to paint does nothing for me, it can occur?

private void pictureBox1_Paint(object sender, PaintEventArgs e)
        {
            label63.Text = Convert.ToString(f);
            label66.Text = Convert.ToString(pinta);

                using (Pen pen = new Pen(Color.Red, 2))
                {
                        if (pinta==true)
                        {
                            //e.Graphics.DrawLine(pen, x1, y1, x2, y2);
                            e.Graphics.DrawLine(pen, 0, 0, 800, 600);
                        }
                }
        }