Const MIN_ASC=65        ‘字母”A”的ASCII值

Function x2D(x As String)As String    ‘字符串小写转成大写

    Dim s As String，zf As String，i As Integer

    S=””

    For i=1 To Len(x)

      zf=Mid(x，i，1)

      If zf>=“a”And zf<=“z”Then

        s=s+    ①   

      Else

        s=s+ zf

      End If

    Next

    X2D=s

 End Function

 Private Sub Command1_Click()

    Dim M As String，K As String，C As String，flag As Boolean

    Dim i As Integer，t As Integer，ch As Integer，pos As Integer·

As Integer

    M=Textl．Text     ‘明文

    K=Text2．Text     ‘密钥

    t=Len(K)

    K=X2D(K)        ‘将密钥全部转成大写

    C=“ ”         ‘加密后的结果

    For i=1 To Len(M)

      ch=Asc(Mid(M，i，1))

      flag=False

      If ch>=97 And ch<=122 Then ch=ch-32：flag=True

      pos=    ②       ‘密钥的字符位置值

      If pos=0 Then pos=t

      j=Asc(Mid(K，pos，1))        ‘密钥字符的ASCII值

      ch=ch-MIN_ASC

      j=j-MIN_ASC

      ch=    ③     

      ch=ch+MIN_ASC

      If flag Then ch=ch+32    ‘设置字母的大小写形式

      C=C & Chr(ch)

    Next i

    Text3．Text=C

End Sub

① ② ③