请求动态图形程序中的问题（已给出程序代码）
Dim i As Single
Dim x As Long, y As Long, a As Long, b As Long
Dim n As Integer, m As Integer, p As Integer, q As Integer
a = 0
b = 0
For i = 0 To 20
a = x
b = y
x = (20 - i) * 90
y = (i / 10) ^ 2 * 120
Picture1.Line (x, y)-(a, b), &HFFFF&
i = i + 1
Next i
Do While i > 20
p = i Mod 20
q = 20 - p
If p = 0 Then
Picture1.Cls
End If
a = x
b = y
x = q * 90
y = (i / 100) ^ 2
Picture1.Line (x, y)-(a, b), &HFFFF&
i = i + 1
Loop
End Sub
设想实现无限动态图形的实现，但该程序运行后总出现溢出，请各位高手予以指点，找出问题之所在，谢谢！
