哪位大神帮忙给下校验和代码

Sub jiaoyan(aa As String)
Dim s1 As String
Dim s2 As String
Dim check(1 To 16) As Integer
Dim i As Integer
Dim X As Integer
Dim rr As Integer
Dim k As Integer
s1 = Len(aa)
If s1 > 0 Then
s2 = aa
Dim check2(1 To 100) As String
Dim check3(1 To 100) As String
For i = 1 To s1
check2(i) = Mid(s2, i, 1)
check3(i) = Asc(check2(i))
k = k + check3(i)
Next i
'Me.Label5.Caption = Hex(k) mod 255mod
' End If
End If
End Sub