void func(void) {
    char texte[] = "Ca change seulement les lettres";
    int i = 0;
    int k = 4;

    while (texte[i]) {
        char c = texte[i];
        if (c >= 'a' && c <= 'z') {
            c = c - 'a';
            c = (c + k) % 26;
            c = c + 'a';
            texte[i] = c;
        } else if (c >= 'A' && c <= 'Z') {
            c = c - 'A';
            c = (c + k) % 26;
            c = c + 'A';
            texte[i] = c;
        }

        i++;
    }

    printf("%s\n", texte);
}