本文为《别怕,Excel VBA其实特别简单(第3版)》随书问题参考答案
以下过程供参考:
Function MidS(ByVal txt, n As Byte) As String
   Application.Volatile True
   Dim T As String, i As Long
   Dim NumStr As String, EnStr As String, Other As String
   For i = 1 To Len(txt)
       T = Mid(txt, i, 1)
       If T Like "[0-9]" Then
            NumStr = NumStr & T
       ElseIf T Like "[A-z]" Then
            EnStr = EnStr & T
       Else
            Other = Other & T
       End If
   Next i
    If n = 0 Then
       MidS = NumStr
    ElseIf n = 1 Then
       MidS = EnStr
    ElseIf n = 2 Then
       MidS = Other
    Else
       MidS = "#参数错误!"
    End If
End Function