Q: I have a problem, my code didn't print anything I am trying to write a code which permits to decode some messages, with the following decoding key : +5, if the number corresponding to the letter in the ascii table is peer and -3 if the number corresponding to the letter in the ascii table is odd : My code is the following : 
public static void main(String[] args) {
    decodeurMessage("undeux");
}
public static String decodeurMessage(String message) {
    String messageDecode = "";
    for(int i=0; i < message.length(); i++) {
        char unCaractere = message.charAt(i);
        int entiercorresp = unCaractere;
        char lettreDecodee;
        if(unCaractere == ' ') {
            lettreDecodee = ' ';
        } else
        if (entiercorresp % 2 == 0) {
            entiercorresp = 97+(entiercorresp - 66)%26;
            lettreDecodee = (char)entiercorresp;
        } else {
            entiercorresp = 97+(entiercorresp - 74)%26;
            lettreDecodee = (char) entiercorresp;
        }

        messageDecode += lettreDecodee;


        }


A: You should add System.out.println(Something you want to be printed);
In your case, I would suspect somethig like that :
public static void main(String[] args) {
    System.out.println(decodeurMessage("undeux"));
}

Another thing. Your method decodeurMessage does not have a return statement. You should have a compilation error.
