'-- สร้างฟังก์ชันเข้ารหัส

Function CaeSarEncrypt(ByVal s As String)
Dim c As String
Dim b As String
Dim a As String
Dim x As String

For i = 1 To s.Length
b = Mid(s, i, 1)
If Asc(b) >= 97 And Asc(b) <= 222 Then
Select Case True
Case b = "x"
a = "a"
Case b = "y"
a = "b"
Case b = "z"
a = "c"
Case Else
a = Chr(Asc(b) + 3)
End Select
Else
Select Case True
Case b = "X"
a = "A"
Case b = "Y"
a = "B"
Case b = "Z"
a = "C"
Case Else
a = Chr(Asc(b) + 3)
End Select
End If

c &= a
Next i

Return c

End Function

'-- สร้างฟังก์ชันถอดรหัส

Function CaeSarDecrypt(ByVal s As String)

Dim c As String
Dim b As String
Dim a As String
Dim x As String

For i = 1 To s.Length
b = Mid(s, i, 1)
If Asc(b) >= 97 And Asc(b) <= 222 Then
Select Case True
Case b = "a"
a = "x"
Case b = "b"
a = "y"
Case b = "c"
a = "z"
Case Else
a = Chr(Asc(b) - 3)
End Select
Else
Select Case True
Case b = "A"
a = "X"
Case b = "B"
a = "Y"
Case b = "C"
a = "Z"
Case Else
a = Chr(Asc(b) - 3)
End Select
End If

c &= a
Next i

Return c

End Function

'-- โค้ดสำหรับปุ่มเข้ารหัส

Private Sub BtnEncrypt_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles BtnEncrypt.Click
TxtEncrypt.Text = CaeSarEncrypt(TxtText.Text)
End Sub

'-- โค้ดสำหรับปุ่มถอดรหัส

Private Sub BtnDecrypt_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles BtnDecrypt.Click
TxtDecrypt.Text = CaeSarDecrypt(TxtEncrypt.Text)
End Sub

'-- โค้ดสำหรับปุ่มเครียร์

Private Sub BtnClear_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles BtnClear.Click
TxtText.Clear()
TxtDecrypt.Clear()
TxtEncrypt.Clear()

End Sub
End Class