OPEN "/dev/stdin" FOR DEVICE AS in

FUNCTION get_odd()

    LOCAL ch, letter

    ch = MEMORY(1)
    GETBYTE ch FROM in

    IF NOT(REGEX(CHR$(PEEK(ch)), "[[:punct:]]")) THEN
        letter = get_odd()
        PRINT CHR$(PEEK(ch));
    ELSE
        letter = PEEK(ch)
    END IF

    FREE ch
    RETURN letter

END FUNCTION

mem = MEMORY(1)
PRINT "Enter string: ";

WHILE TRUE

    GETBYTE mem FROM in
    PRINT CHR$(PEEK(mem));

    IF REGEX(CHR$(PEEK(mem)), "[[:punct:]]") THEN
        IF PEEK(mem) <> 46 THEN
            POKE mem, get_odd()
            PRINT CHR$(PEEK(mem));
        END IF
        IF PEEK(mem) = 46 THEN BREAK
    END IF
WEND

FREE mem
CLOSE DEVICE in

PRINT