PROGRAM ROT13

BEGIN
INPUT("Enter a string ",TEXT$)
FOR C%=1 TO LEN(TEXT$) DO
    A%=ASC(MID$(TEXT$,C%,1))
    CASE A% OF
            65..90->
                   MID$(TEXT$,C%,1)=CHR$(65+(A%-65+13) MOD 26)
            END ->
            97..122->
                   MID$(TEXT$,C%,1)=CHR$(97+(A%-97+13) MOD 26)
            END ->
    END CASE
END FOR
PRINT("Converted: ";TEXT$)
END PROGRAM