Moving ball

% /////////////////////
% // Michael Yazdani //
% /////////////////////
% // ICS 3U ///////////
% /////////////////////

setscreen ("graphics:700;700")

% VARIABLE AND CONSTANT DECLARATIONS

var x, y : int
const inc := 8
const radius := 25
var chars : array char of boolean

% FORWARD DECLARATIONS

forward procedure moveup
forward procedure movedown
forward procedure moveleft
forward procedure moveright

% PROCEDURES

procedure keydown               % determines what keys are being pressed
    Input.KeyDown (chars)
end keydown

procedure circle                % draws a circle at location x and y with radius "radius" then erases for next frame
    drawoval (x, y, radius, radius, 1)
    delay (16)
    drawoval (x, y, radius, radius, white)
end circle

body procedure moveup           % sets y to y + inc (5 pixels), if y is greater than the vertical resolution of the output window - radius, movedown is called
    loop
        keydown
        exit when chars (KEY_LEFT_ARROW) or chars (KEY_RIGHT_ARROW) or chars (KEY_DOWN_ARROW) or chars (KEY_ESC)
        y := y + inc
        if y > maxy - radius then
            movedown
        end if
        circle
    end loop
end moveup

body procedure movedown         % sets y to y - inc,  if y is less than radius (in this case, 25 pixels), moveup is called
    loop
        keydown
        exit when chars (KEY_LEFT_ARROW) or chars (KEY_RIGHT_ARROW) or chars (KEY_UP_ARROW) or chars (KEY_ESC)
        y := y - inc
        if y < radius then
            moveup
        end if
        circle
    end loop
end movedown

body procedure moveright        % sets x to x + inc, if x is greater than the horizontal resolution of the output window, moveleft is called
    loop
        keydown
        exit when chars (KEY_LEFT_ARROW) or chars (KEY_UP_ARROW) or chars (KEY_DOWN_ARROW) or chars (KEY_ESC)
        x := x + inc
        if x > maxx - radius then
            moveleft
        end if
        circle
    end loop
end moveright

body procedure moveleft         % sets x to x - inc, if x is less than radius, moveright is called
    loop
        keydown
        exit when chars (KEY_RIGHT_ARROW) or chars (KEY_UP_ARROW) or chars (KEY_DOWN_ARROW) or chars (KEY_ESC)
        x := x - inc
        if x < radius then
            moveright
        end if
        circle
    end loop
end moveleft

% VARIABLE INITILIZATION

x := maxx div 2                 % initializes x to center of output window
y := maxy div 2                 % initializes y to center of output window

% MAIN PROGRAM

loop
    keydown
    exit when chars (KEY_ESC)   % exits main loop, terminates program
    if chars (KEY_LEFT_ARROW) then
        moveleft
    elsif chars (KEY_RIGHT_ARROW) then
        moveright
    elsif chars (KEY_DOWN_ARROW) then
        movedown
    elsif chars (KEY_UP_ARROW) then
        moveup
    end if
    moveup
end loop

cls
put "Program Terminated."