半角と全角を判定するには

Public Function IsNarrow(strText As String) As Boolean
    Dim intCode As Integer

    For i = 1 To Len(strText)
         intCode = Asc(Mid(strText, i, 1))

         If intCode < &H0 Or &HFF < intCode Then
            IsNarrow = False

            Exit Function

         End If

    Next

    IsNarrow = True

End Function

Public Function IsWide(strText As String) As Boolean
    Dim intCode As Integer

    For i = 1 To Len(strText)
         intCode = Asc(Mid(strText, i, 1))

         If &H0 <= intCode And intCode <= &HFF Then
            IsWide = False

            Exit Function

         End If

    Next

    IsWide = True

End Function

Private Sub Test()
    Debug.Assert IsNarrow(" ")
    Debug.Assert IsNarrow("0")
    Debug.Assert IsNarrow("A")
    Debug.Assert IsNarrow("a")
    Debug.Assert IsNarrow("~")
    Debug.Assert IsNarrow("｡")
    Debug.Assert IsNarrow("ｦ")
    Debug.Assert IsNarrow("ﾝ")
    Debug.Assert IsNarrow("ﾟ")
    Debug.Assert IsNarrow(" 0Aa~｡ｦﾝﾟ")

    Debug.Assert IsNarrow("　") = False
    Debug.Assert IsNarrow("０") = False
    Debug.Assert IsNarrow("Ａ") = False
    Debug.Assert IsNarrow("ａ") = False
    Debug.Assert IsNarrow("あ") = False
    Debug.Assert IsNarrow("ア") = False
    Debug.Assert IsNarrow("亜") = False
    Debug.Assert IsNarrow("　０Ａａあア亜") = False

    Debug.Assert IsWide("　")
    Debug.Assert IsWide("０")
    Debug.Assert IsWide("Ａ")
    Debug.Assert IsWide("ａ")
    Debug.Assert IsWide("あ")
    Debug.Assert IsWide("ア")
    Debug.Assert IsWide("亜")
    Debug.Assert IsWide("　０Ａａあア亜")

    Debug.Assert IsWide(" ") = False
    Debug.Assert IsWide("0") = False
    Debug.Assert IsWide("A") = False
    Debug.Assert IsWide("a") = False
    Debug.Assert IsWide("~") = False
    Debug.Assert IsWide("｡") = False
    Debug.Assert IsWide("ｦ") = False
    Debug.Assert IsWide("ﾝ") = False
    Debug.Assert IsWide("ﾟ") = False
    Debug.Assert IsWide(" 0Aa~｡ｦﾝﾟ") = False

End Sub