s$ = "nowhere ABJURER"
print " Cadena original : ", s$
print "  Tras codificar : ", Rot13$(s$)
print "Tras decodificar : ", Rot13$(Rot13$(s$))
end

sub Rot13$ (s$)
    local cad$
    cad$ = ""

    for i = 1 to len(s$)
        temp = asc(mid$(s$, i, 1))

        if temp >= 65 and temp <= 90 then      // A to Z
            temp = (mod((temp - 52), 26)) + 65
        elsif temp >= 97 And temp <= 122 then  // a to z
            temp = (mod((temp - 84), 26)) + 97
        end if
        cad$ = cad$ + chr$(temp)
    next i
    return cad$
end sub