请教vb高手

Const c = 3000
Dim a(c) As Single
Dim i, j As Single
Dim b As Single
Dim p, q, As Single
j = -2500
For i = -5000 To -30
j = j + 100
i = i + 100
p = Sqr(i ^ 2 + j ^ 2)
If p > 2000 And p <= 4000 Then
q = 94.4 + (88.8 - 94.4) / (Log(4000) - Log(2000)) * (Log(p) - Log(2000))
ElseIf p > 4000 And p <= 6300 Then
q = 88.8 + (84.8 - 88.8) / (Log(6300) - Log(2000)) * (Log(p) - Log(2000))
ElseIf p <= 10000 And p > 6300 Then
q = 84.8 + (80.3 - 84.8) / (Log(10000) - Log(6300)) * (Log(p) - Log(6300))
ElseIf p <= 16000 And p > 10000 Then
q = 80.3 + (76.1 - 80.3) / (Log(16000) - Log(10000)) * (Log(p) - Log(10000))
ElseIf p <= 25000 And p > 16000 Then
q = 76.1 + (71.2 - 76.1) / (Log(25000) - Log(16000)) * (Log(p) - Log(16000))
End If
a(c) = q + 7
要画出a（c）和p的关系图，还要是关于a(c)的等值线，又没有人给指点阿

等着急用,,如有会的请帮忙,谢谢哈