qsort(books, n, sizeof(Book), compareBooksByYearOfPublication);

int compareBooksByYearOfPublication(void *p1, void *p2)
{
    Book *book1 = (Book *)p1;
    Book *book2 = (Book *)p2;

    if (book1->yearOfPublication < book2->yearOfPublication) {
        return -1;
    } else if (book1->yearOfPublication > book2->yearOfPublication) {
        return 1;
    } else {
        return 0;
    }
}