void del_book_info(book* b){
    b->title = "";
    b->author = "";

    int i, j;
    for(i = 0; i < DEFAULT_SIZE; i++){
        for(j = i+1; j < DEFAULT_SIZE; j++){
	    if(heap[i].author=="" && heap[i].title=="" && heap[j].author=="" && heap[j].title==""){
                heap[i].year = j;
	   	j = DEAFULT_SIZE;
	    }
        }
 	if(i==DEFAULT_SIZE-1 && heap[i].author=="" && heap[i].title==""){
	    heap[i].year = -1;
	}
    }
}