Function zz(z As String) As String
Select Case z
Case "a1","a2","a3"
zz = "A"
Case "b1","b2","b3"
zz = "B"
Case Else
zz = "zzzz"
End Select
End Function
上述代码,如果z是空值的话,zz(z)不会输出"zzzz",而是输出"# 错误"。必须采用zz(nz(z))才能正常。
但如果把上述代码中"z as string"中的定义去掉,就可以直接使用zz(z)了。
为何?
Function zz(Optinal z As String) As String
Select Case z
Case "a1","a2","a3"
zz = "A"
Case "b1","b2","b3"
zz = "B"
Case Else
zz = "zzzz"
End Select
End Function