Imports System

Imports Microsoft.VisualBasic

​

Public Module Module1

    Public Sub Main()

        Console.WriteLine("Caesar Cipher Encoder/Decoder")

        Dim PlainText as String

        Dim CipherText as String

        Dim Letter as String

        Dim Ascii as Integer

        Dim Offset as Integer

        Dim Choice as Integer

        CipherText = ""

        Console.WriteLine("Enter the text you want encoded / decoded: ")

        PlainText = Console.ReadLine()

        Console.WriteLine("Press 1 to encode or press 2 to decode: ")

        Choice = Console.ReadLine()

​

        Console.WriteLine("Enter a value between 1 and 25: ")

        Offset = Console.ReadLine()

        If Choice = 1 then

            'Here it encodes character by character

            For n = 0 to PlainText.Length -1

            Letter = PlainText.Chars(n)

                Ascii = Asc(Letter)

                'Here it creates a range for uppercase letters according to ascii

                If Ascii >= 65 And Ascii <= 90 then

                    If Ascii + Offset <= 90 then

                        Ascii = Ascii + Offset

                    Else

                        'Here it wraps around from z to a

                        Ascii = Ascii + Offset - 26

                    End If

                'Here it creates a range for lowercase letters according to ascii

                Else If Ascii >= 97 And Ascii <= 122 then

                    If Ascii + Offset <= 122 then

                        Ascii = Ascii + Offset

                    Else

                        'Here it wraps around from z to a

                        Ascii = Ascii + Offset - 26

                    End If

                End If

                CipherText = CipherText + Chr(Ascii)

            Next n

        Else

            'Here it decodes character by character

            For n = 0 to PlainText.Length -1

                Letter = PlainText.Chars(n)

                Ascii = Asc(Letter)

                'Here it creates a range for uppercase letters according to ascii

                If Ascii >= 65 And Ascii <= 90 then

                    If Ascii - Offset >= 65 then

                        Ascii = Ascii - Offset

                    Else

                        'Here it wraps around from z to a

                        Ascii = Ascii - Offset + 26

                    End If

                'Here it creates a range for lowercase letters according to ascii

                Else If Ascii >= 97 And Ascii <= 122 then

                    If Ascii - Offset >= 97 then

                        Ascii = Ascii - Offset

                    Else

                        'Here it wraps around from z to a

                        Ascii = Ascii - Offset + 26

                    End If

                End If

                CipherText = CipherText + Chr(Ascii)

            Next n

        End If

        Console.Writeline(CipherText)

    End Sub

End Module