如何循环特定的字符串凯撒密码 vb10

Question

我正在创建一个具有加密和解密功能的程序。问题是它应该只适用于代码上的静态字符串。当输入的纯文本是最后一个时，它应该循环。例如，当我输入 0 且密钥为 2 时，字符串为“ABCDE...Z1234567890”，密文应为 B。我有四个文本框用于密钥、输入、明文和密文。这是我的代码。

Public Class Form1
       Dim key As Integer
Const Intext As String = "abcdefghijklmnopqrstuvwxyz1234567890"
Private Sub btCipher_Click(sender As Object, e As EventArgs) Handles btCipher.Click

    Dim plain, s, r As String
    Dim i, j As Long
    key = Val(txtKey.Text)
    plain = txtInput.Text
    For i = 1 To Len(plain)
        r = Mid$(plain, i, 1)
        j = (InStr(1, Intext, r))
        If key > 36 Then
            s = s & Mid$(Intext, j + (key - 36), 1)
        Else
            s = s & Mid$(Intext, j + key, 1)
        End If

    Next i

    txtResult.Text = s
End Sub

Private Sub btDecipher_Click(sender As Object, e As EventArgs) Handles btDecipher.Click

    Dim plain, s, r As String
    Dim i, j As Long
    key = Val(txtKey.Text)
    plain = txtResult.Text
    For i = 1 To Len(plain)
        r = Mid$(plain, i, 1)
        j = (InStr(1, Intext, r))
        If key > 36 Then
            s = s & Mid$(Intext, j + (key - 36), 1)
        Else
            s = s & Mid$(Intext, j - key, 1)
        End If
    Next i

    txtText.Text = s
End Sub End Class

我的问题是它没有循环。也许有人可以帮忙。谢谢。

Answer 1

我不确定您的代码为什么不起作用，但请尝试以下代码：

Public Class Form1

    Const Intext As String = "abcdefghijklmnopqrstuvwxyz1234567890"

    Private Function Transcode(text As String, map As Dictionary(Of Char, Char)) As String
        Return New String(text.Select(Function(x) If(map.ContainsKey(x), map(x), x)).ToArray())
    End Function

    Private Sub btCipher_Click(sender As Object, e As EventArgs) Handles btCipher.Click
        Dim key = Val(txtKey.Text)
        Dim map = _
            Intext _
                .Zip(Intext.ToCharArray().Concat(Intext.ToCharArray()).Skip(key), Function(f, t) New With {f, t}) _
                .ToDictionary(Function(x) x.f, Function(x) x.t)
        txtResult.Text = Transcode(txtInput.Text, map)
    End Sub

    Private Sub btDecipher_Click(sender As Object, e As EventArgs) Handles btDecipher.Click
        Dim key = Val(txtKey.Text)
        Dim map = _
            Intext _
                .Zip(Intext.ToCharArray().Concat(Intext.ToCharArray()).Skip(key), Function(f, t) New With {f, t}) _
                .ToDictionary(Function(x) x.t, Function(x) x.f)
        txtText.Text = Transcode(txtResult.Text, map)
    End Sub

End Class

我已经测试了算法，它运行良好。