Excel VBA 質問スレ Part19

以下はセルに円を描画するマクロ　？？？に入る式を答えよ

Sub en(tx, ty, hankei) '中心X 中心Y 半径
Dim a, b, c, d, e, f, g, z
a = hankei ^ 2
b = hankei
c = 0
Do
If b > 0 Then
d = -1
Else
d = 1
End If
If c > 0 Then
e = 1
Else
e = -1
End If
f = Abs(b ^ 2 + (c + d) ^ 2 - a)
g = ？？？
If f > g Then
b = b + e
Else
c = c + d
End If
Cells(c + ty, b + tx).Interior.Color = 0
If c = 0 And e = 1 Then Exit Sub
Loop
End Sub