need help with the screem

[mathgenius]

I'm doing the christmas house project. i have several problems.

hope someone can help me:D
the first problem:
I want to create a moon moving along a quadratic equation. but the problem comes from the quadratic equation. this problem i cannot fully explain. i hope someone can look up my code. make the moon goes constantly.

the second problem:
the screem is keep flashing as the moon goes by.

below is my code:
View.Set("offscreenonly")
View.Set("graphics:1000,700")
colourback (7)
cls


type FlakeType : %This is a type d
record
x, y, speed, size : real
end record



var x, y, button : int := 0
var size : int := 200
var inuse : boolean := false
var Snow : array 1 .. size of FlakeType
const delaytime := 1000000

var aa,bb,aaa,bbb,aaaa,bbbb,aaaaa,bbbbb : int
var c,d,cc,dd,ccc,ddd,cccc,dddd:int
var q : int

procedure DrawBack

randint(aa, 1, maxx)
randint(bb, 400,maxx)
randint(aaa,1,maxx)
randint(bbb,400,maxx)
randint(aaaa,1,maxx)
randint(bbbb,400,maxx)
randint(aaaaa,1,maxx)
randint(bbbbb,400,maxx)
drawfillstar(aa,bb,aa+8,bb+8,white)
drawfillstar(aaa,bbb,aaa+8,bbb+8,white)
drawfillstar(aaaa,bbbb,aaaa+8,bbbb+8,white)
drawfillstar(aaaaa,bbbb,aaaaa+8,bbbb+8,white)




drawfilloval (500, 10, 500, 70, grey)
drawfilloval (240, 250, 90, 110, green)
drawfillbox (330, 250, 400, 350, 15)
drawfillbox (150, 50, 400, 250, blue)
drawfillbox (290, 50, 360, 190, 4)
drawline (290, 120, 360, 120, brown)
drawline (290, 121, 360, 121, brown)
drawline (290, 122, 360, 122, brown)
drawfilloval (305, 130, 5, 5, brown)
drawfillbox (180, 140, 240, 200, yellow)
drawline (210, 140, 210, 200, black)
drawfilloval (550, 50, 60, 36, white)
drawfilloval (550, 60, 5, 5, black)
drawfilloval (550, 95, 50, 30, white)
drawfilloval (550, 95, 5, 5, black)
drawfilloval (550, 130, 35, 23, white)
drawfilloval (550, 130, 5, 5, black)
drawfilloval (550, 182, 40, 40, white)
drawfilloval (550, 175, 3, 6, red)
drawfilloval (550, 222, 50, 20, blue)
drawfillbox (527, 232, 573, 270, 1)
drawfilloval (535, 190, 4, 4, 1)
drawfilloval (565, 190, 4, 4, 1)
drawfilloval (550, 164, 8, 2, 67)
drawfilloval (850, 70, 60, 36, green)
drawfilloval (850, 115, 50, 30, green)
drawfilloval (850, 150, 35, 23, green)
drawfilloval (850, 175, 20, 40, green)
drawfillstar (830, 200, 875, 245, yellow)

randint(q,1,20)
randint(c,790,910)
randint(cc,790,910)
randint(ccc,790,910)
randint(cccc,790,910)
randint(d,34,215)
randint(dd,34,215)
randint(ddd,34,215)
randint(dddd,34,215)
drawfillstar(c,d,c+6,d+6,q)
drawfillstar(cc,dd,cc+4,dd+4,q)
drawfillstar(ccc,ddd,ccc+5,ddd+5,q)
drawfillstar(cccc,dddd,cccc+4,dddd+4,q)


end DrawBack



procedure GenerateFlakeArray
for i : 1 .. size
Snow (i).x := Rand.Int (0, maxx)
Snow (i).y := Rand.Int (0, maxy)
Snow (i).speed := Rand.Real * Rand.Int (1, 3)
Snow (i).size := Snow (i).speed
end for
end GenerateFlakeArray
process GenerateX
if (not (inuse)) then
x := Rand.Int (-600, 600)
inuse := true
delay (2500)
inuse := false
end if
end GenerateX
process LetItSnow
loop

fork GenerateX
for i : 1 .. size
if x < 500 and x > 300 then
x := 0
elsif x < 600 and x > 500 then
x := 200
elsif x < 700 and x > 600 then
x := 400
elsif x < 800 and x > 700 then
x := 600
elsif x < 300 and x > 200 then
x := -200
elsif x < 200 and x > 100 then
x := -400
elsif x < 100 and x > 0 then
x := -600
end if
Snow (i).y -= Snow (i).speed
Snow (i).x += round (x / 100)
if Snow (i).y < 0 then
Snow (i).y := Rand.Int (maxy, maxy + 100)
end if
if Snow (i).x > maxx then
Snow (i).x := Rand.Int (-10, 0)
end if
if Snow (i).x < 0 then
Snow (i).x := Rand.Int (maxx, maxx + 100)
end if
drawfilloval (round (Snow (i).x), round (Snow (i).y), round (Snow (i).size), round (Snow (i).size), white)
end for
View.Update
for o : 1 .. size
drawfilloval (round (Snow (o).x), round (Snow (o).y), round (Snow (o).size), round (Snow (o).size), blue)
end for
DrawBack %Prevents scratching the whole picture
end loop
end LetItSnow





%Main function:
%Draw the initial black background.
GenerateFlakeArray %Generate the snow flake array.
fork LetItSnow %Let it snow!


var hl1, hl2 : int


loop
for i : 1 .. 30
hl1 := (i) * 36
hl2 := 610 - (15 - (i)) ** 2

cls
drawfilloval (hl1, hl2, 58, 58, yellow)
drawfilloval (hl1, hl2, 55, 55, black)
drawfilloval (hl1, hl2, 52, 52, yellow)
drawfilloval (hl1, hl2, 49, 49, black)
drawfilloval (hl1, hl2, 46, 46, yellow)
drawfilloval (hl1, hl2, 43, 43, black)
drawfilloval (hl1, hl2, 40, 40, yellow) %------------------------moon
delay(300)


end for
View.Update

end loop

[Albrecd]

The first thing you could do that would drasticly help your ability to debug your code, would be to change your variable names. aa, aaa, aaaa, etc. are very similar, and get confusing fast, as well as not being at all descriptive.

About the choppy motion of the moon. The reason this occurs is that you're moving it a large number of pixels (36 in the x-axis alone) every frame, with a large delay between frames (0.3 seconds). Decreasing the distance and delay will make the movement much smoother.

As for your error with your quadratic formula, I'm not entirely sure what you are referring to; the moon does travel in a parabola. Please specify the error.