void Main(){    while (true)    {        Console.WriteLine ("请输入标题或作者");        var key = Console.ReadLine().Trim();            Library.Search(key).Dump();        Console.WriteLine ("请输入要借阅/归还的图书编号");        var id = Convert.ToInt32(Console.ReadLine());        var book = Library.Search(id);                Library.ChangeStatus(book);                Console.WriteLine ("是否继续？Y/N");        if (Console.ReadLine().ToLower()!="Y".ToLower())        {            break;        }    }}class Library{    private static readonly List<Book> Books = new List<Book>{        new Book(1,"红楼梦","曹雪芹",Status.已归还),        new Book(2,"西游记","吴承恩",Status.已归还),        new Book(3,"水浒传","施耐庵",Status.已归还),        new Book(4,"三国演义","罗贯中",Status.已归还)    };        public static IEnumerable<Book> Search(string key){        foreach (var book in Books)        {            if (book.Title.Contains(key) || book.Author.Contains(key))            {                yield return book;            }        }            }        public static Book Search(int id){        foreach (var book in Books)        {            if (book.Id==id)            {                return book;            }        }        return null;    }        public static void ChangeStatus(Book book){        if (book!=null)        {            if (book.Status==Status.已归还)            {                Console.WriteLine ("图书借阅成功");                book.Status=Status.已借阅;            }else            {                Console.WriteLine ("图书归还成功");                book.Status=Status.已归还;            }        }    }}class Book{    public int Id;    public string Title;    public string Author;    public Status Status;        public Book(int id,string title,string author,Status status){        Id=id;        Title = title;        Author = author;        Status = status;    }        public string Info(){        return string.Format("Id:{0}\tTitle:{1}\tAuthor:{2}\tStatus:{3}",Title,Author,Status);    }}enum Status{    已借阅,已归还}