怎樣用vb的if語句寫壹個判斷字母是否為大小寫的程序?

a = "A"

If Asc(a) > 64 And Asc(a) < 91 Then

MsgBox "大寫字母"

ElseIf Asc(a) > 96 And Asc(a) < 123 Then

MsgBox "小寫字母"

Else

MsgBox "非字母"

End If

或

If a >= "A" And a <= "Z" Then

MsgBox "大寫字母"

ElseIf a >= "a" And a <= "z" Then

MsgBox "小寫字母"

Else

MsgBox "非字母"

End If

或

If LCase(a) <> a Then

MsgBox "大寫字母"

ElseIf UCase(a) <> a Then

MsgBox "小寫字母"

Else

MsgBox "非字母"

End If