Declare.s Rot13(text_to_code.s)

If OpenConsole()
  Define txt$

  Print("Enter a string to encode: "): txt$=Input()

  PrintN("Coded  : "+Rot13(txt$))
  PrintN("Decoded: "+Rot13(Rot13(txt$)))

  Print("Press ENTER to quit."): Input()
  CloseConsole()
EndIf

Procedure.s Rot13(s.s)
  Protected.i i
  Protected.s t, u
  For i=1 To Len(s)
    t=Mid(s,i,1)
    Select Asc(t)
      Case Asc("a") To Asc("m"), Asc("A") To Asc("M")
        t=chr(Asc(t)+13)
      Case Asc("n") To Asc("z"), Asc("N") To Asc("Z")
        t=chr(Asc(t)-13)
    EndSelect
    u+t
  Next
  ProcedureReturn u
EndProcedure