loop
    mousewhere (mx, my, mb)
    if mb = 1 and mx > 10 and mx < 70 and my > 10 and my < 70 then
        tool := "pencil"
    elsif tool = "pencil" and mb = 1 and pen = 0 and mx > 180 and mx < 990 and my > 10 and my < 550 then
        drawdot (mx, my, col)
        pen := 1
        oldx := mx
        oldy := my
    elsif mb = 1 and pen = 1 and tool = "pencil" and mx > 180 and mx < 990 and my > 10 and my < 550 then
        drawdot (mx, my, col)
        drawline (mx, my, oldx, oldy, col)
        pen := 1
        oldx := mx
        oldy := my
    elsif mb = 0 and pen = 1 and tool = "pencil" and mx > 180 and mx < 990 and my > 10 and my < 550 then
        pen := 0