moving ball - getch

var x, x1, y, y1, button : int
const keyleft := chr (203)
const keyright := chr (205)
const keydown := chr (208)
const keyup := chr (200)
const inc := 5
const radius := 25
var chars : string (1)

x := radius
y := radius
setscreen ("graphics800:800")
loop
    Mouse.Where (x1, y1, button)
    drawoval (x, y, radius, radius, 1)
    if button = 1 then
        Mouse.Where (x, y, button)
        drawoval (x, y, radius, radius, 1)
    elsif button = 0 then
        drawoval (x, y, radius, radius, 1)
        getch (chars)
        drawoval (x, y, radius, radius, white)
        if chars = keyleft then
            x := x - inc
            if x < radius then
                x := radius
            end if
        elsif chars = keyright then
            x := x + inc
            if x > maxx - radius then
                x := maxx - radius
            end if
        elsif chars = keydown then
            y := y - inc
            if y < radius then
                y := radius
            end if
        elsif chars = keyup then
            y := y + inc
            if y > maxy - radius then
                y := maxy - radius
            end if
        end if
        %put ""
    end if
end loop