c.frm

在网上看到此代码很实用

VERSION 5.00
Begin VB.Form Form1 
   BorderStyle     =   3  'Fixed Dialog
   Caption         =   "凯撒加密(密钥k=3)"
   ClientHeight    =   2205
   ClientLeft      =   45
   ClientTop       =   435
   ClientWidth     =   4005
   LinkTopic       =   "Form1"
   MaxButton       =   0   'False
   MinButton       =   0   'False
   ScaleHeight     =   2205
   ScaleWidth      =   4005
   ShowInTaskbar   =   0   'False
   StartUpPosition =   3  '窗口缺省
   Begin VB.CommandButton Command2 
      Caption         =   "开始解密"
      Height          =   375
      Left            =   2400
      TabIndex        =   5
      Top             =   1560
      Width           =   975
   End
   Begin VB.CommandButton Command1 
      Caption         =   "开始加密"
      Height          =   375
      Left            =   1080
      TabIndex        =   2
      Top             =   1560
      Width           =   975
   End
   Begin VB.TextBox Text2 
      Height          =   375
      Left            =   1080
      TabIndex        =   1
      Top             =   960
      Width           =   2535
   End
   Begin VB.TextBox Text1 
      Height          =   375
      Left            =   1080
      TabIndex        =   0
      Top             =   240
      Width           =   2535
   End
   Begin VB.Label Label2 
      Caption         =   "密文："
      Height          =   255
      Left            =   240
      TabIndex        =   4
      Top             =   960
      Width           =   615
   End
   Begin VB.Label Label1 
      Caption         =   "明文："
      Height          =   255
      Left            =   240
      TabIndex        =   3
      Top             =   240
      Width           =   735
   End
End
Attribute VB_Name = "Form1"
Attribute VB_GlobalNameSpace = False
Attribute VB_Creatable = False
Attribute VB_PredeclaredId = True
Attribute VB_Exposed = False
Private Sub Command1_Click()
Dim mw As String
Dim m As String
Dim k As Integer
Dim n As Integer
Dim i As Long
Dim tmp As String
If Text1.Text = "" Then
MsgBox "请输入明文。"
Text1.SetFocus
Exit Sub
End If
k = 4
n = 26
mw = Text1.Text

For i = 1 To Len(mw)
tmp = Mid(mw, i, 1)
tmp = f(tmp, k, n)
If tmp <> "error" Then
m = m + tmp
Else
MsgBox "字符串中含有非法字符,只能为英文字母！"
Text1.SetFocus
Exit Sub
End If
Next i
Text2.Text = m
End Sub

Private Function f(ByVal a As String, k As Integer, n As Integer) As String
If ((Asc(a) >= 65 And Asc(a) <= 97) Or (Asc(a) >= 97 And Asc(a) <= 122)) And Len(a) = 1 Then
If Asc(a) >= 65 And Asc(a) <= 97 Then f = Chr((Asc(a) - 64 + k) Mod n + 64)
If Asc(a) >= 97 And Asc(a) <= 122 Then f = Chr((Asc(a) - 96 + k) Mod n + 96)
Else
f = "error"
End If
End Function


Private Function j(ByVal a As String, k As Integer, n As Integer) As String
If ((Asc(a) >= 65 And Asc(a) <= 97) Or (Asc(a) >= 97 And Asc(a) <= 122)) And Len(a) = 1 Then
If Asc(a) >= 65 And Asc(a) <= 97 Then j = Chr((Asc(a) - 64 - k) Mod n + 64)
If Asc(a) >= 97 And Asc(a) <= 122 Then j = Chr((Asc(a) - 96 - k) Mod n + 96)
Else
j = "error"
End If
End Function

Private Sub Command2_Click()
Dim mw As String
Dim m As String
Dim k As Integer
Dim n As Integer
Dim i As Long
Dim tmp As String
If Text2.Text = "" Then
MsgBox "请输入密文"
Text2.SetFocus
Exit Sub

End If
k = 4
n = 26
mw = Text2.Text

For i = 1 To Len(mw)
tmp = Mid(mw, i, 1)
tmp = j(tmp, k, n)
If tmp <> "error" Then
m = m + tmp
Else
MsgBox "字符串中含有非法字符,只能为英文字母！"
Text2.SetFocus
Exit Sub
End If
Next i
Text1.Text = m
End Sub