依次输入一元二次多项式的二次项，一次项和常数项系数，输入它的两个实根

Private Sub Command1_Click()
a = Text1.Text
b = Text2.Text
c = Text3.Text
d = (b ^ 2 - 4 * a * c)
If a = 0 Then
MsgBox ("a不能为0")
Else
If d >= 0 Then
Label1.Caption = "实数根如下"
X1 = (-b + Sqr(d)) / (2 * a)
X2 = (-b - Sqr(d)) / (2 * a)
Text4.Text = abc(Round(X1, 2))
Text5.Text = abc(Round(X2, 2))
ElseIf d < 0 Then
Label1.Caption = "虚数根如下"
aa = (-b / (2 * a))
bb = Sqr(Abs(d)) / (2 * a)
Text4.Text = abc(Round(aa, 2)) & "+" & abc(Round(bb, 2)) & "i"
Text5.Text = abc(Round(aa, 2)) & "-" & abc(Round(bb, 2)) & "i"
End If
End If
End Sub
Function abc(n)
If Abs(n) < 1 Then
If n > 0 Then
abc = "0" & n
Else
abc = "-0" & Abs(n)
End If
Else
abc = n
End If
End Function
其中的小数