Sub Rot13
  EncodedString = ""
  For i = 1 To Text.GetLength(String)
    Code = Text.GetCharacterCode(Text.GetSubText(String, i, 1))
    If Code >= 65 And Code <= 90 Then
      EncodedCode = Code + 13
      If EncodedCode > 90 Then
        EncodedCode = 64 + EncodedCode - 90
      EndIf
    ElseIf Code >= 97 And Code <= 122 Then
      EncodedCode = Code + 13
      If EncodedCode > 122 Then
        EncodedCode = 96 + EncodedCode - 122
      EndIf
    Else
      EncodedCode = Code
    EndIf
    EncodedString = EncodedString + Text.GetCharacter(EncodedCode)
  EndFor
EndSub

String = "Rosetta Code"
Rot13()
TextWindow.WriteLine(EncodedString)