【加试题】完善如下功能的Visual Basic程序：在文本框Text1中输入一个偶数，单击“求解”按钮Command1，将这个偶数拆分成二个素数之和。请完成下面两个小题。

程序代码如下：

Private Sub Command1_Click()

  Dim n As Integer, i As Integer

  List1.Clear

  n = Val(Text1.Text)

  If n Mod 2 = 0 Then

    For i = 2 To Int(n / 2)

     If isodd(i) = (isodd(n - i)) Then

        List1.AddItem Str(n) + " =" + Str(i) + " +" + Str(n - i)

      End If

    Next i

  Else

    Text1.Text = Str(n) + "不是偶数！"

  End If

End Sub

Private Function isodd(n As Integer) as boolean

   Dim f As integer

   f = 0

   For i = 2 To Sqr(n)

     If n Mod i = 0 Then f = 1: Exit For

   Next i

  isodd =  f

End Function