c#库管理控制台程序

Question

在这段代码中，当我添加2本书并尝试删除第1本和第2本时，第1本被删除，第2本没有。在下一种情况下，当我添加3本书并逐一删除时，1本被删除，2本没有，当我删除2本时，第三本不见了。当我添加4本书2和4未删除。

我的代码(我是实习生，所以我是c#的初学者)

using System;
using System.Collections.Generic;
namespace LibraryManagement
{
    //Defining a class Book
    class Book
    {
        public int bookId;
        public string bookName;
        public int bookPrice;
        public int bookCount;
        public int x;
    }
    //Defining a class Borrow
    class BorrowDetails
    {
        public int userId;
        public string userName;
        public string userAddress;
        public int borrowBookId;
        public DateTime borrowDate;
        public int borrowCount;
    }
    class Program
    {
        static List<Book> bookList = new List<Book>();
        static List<BorrowDetails> borrowList = new List<BorrowDetails>();
        static Book book = new Book();
        static BorrowDetails borrow = new BorrowDetails();
        //Password verfication and Menu 
        static void Main(string[] args)
        {
            Console.Write("Welcome !!!nEnter your password :");
            string password = Console.ReadLine();
            if (password == "sync")
            {
                bool close = true;
                while (close)
                {
                    Console.WriteLine("nMenun" +
                    "1)Add bookn" +
                    "2)Delete bookn" +
                    "3)Search bookn" +
                    "4)Borrow bookn" +
                    "5)Return bookn" +
                    "6)Closenn");
                    Console.Write("Choose your option from menu :");
                    int option = int.Parse(Console.ReadLine());
                    if (option == 1)
                    {
                        GetBook();
                    }
                    else if (option == 2)
                    {
                        RemoveBook();
                    }
                    else if (option == 3)
                    {
                        SearchBook();
                    }
                    else if (option == 4)
                    {
                        Borrow();
                    }
                    else if (option == 5)
                    {
                        ReturnBook();
                    }
                    else if (option == 6)
                    {
                        Console.WriteLine("Thank you");
                        close = false;
                        break;
                    }
                    else
                    {
                        Console.WriteLine("Invalid optionnRetry !!!");
                    }
                }
            }
            else
            {
                Console.WriteLine("Invalid password");
            }
            Console.ReadLine();
        }
        //To add book details to the Library database
        public static void GetBook()
        {
            Book book = new Book();
            Console.WriteLine("Book Id:{0}", book.bookId = bookList.Count + 1);
            Console.Write("Book Name:");
            book.bookName = Console.ReadLine();
            Console.Write("Book Price:");
            book.bookPrice = int.Parse(Console.ReadLine());
            Console.Write("Number of Books:");
            book.x = book.bookCount = int.Parse(Console.ReadLine());
            bookList.Add(book);
        }
        //To delete book details from the Library database 
        public static void RemoveBook()
        {
            Book book = new Book();
            Console.Write("Enter Book id to be deleted : ");
            int Del = int.Parse(Console.ReadLine());
            if (bookList.Exists(x => x.bookId == Del))
            {
                bookList.RemoveAt(Del - 1);
                Console.WriteLine("Book id - {0} has been deleted", Del);
            }
            else
            {
                Console.WriteLine("Invalid Book id");
            }
            bookList.Add(book);
        }
        //To search book details from the Library database using Book id 
        public static void SearchBook()
        {
            Book book = new Book();
            Console.Write("Search by BOOK id :");
            int find = int.Parse(Console.ReadLine());
            if (bookList.Exists(x => x.bookId == find))
            {
                foreach (Book searchId in bookList)
                {
                    if (searchId.bookId == find)
                    {
                        Console.WriteLine("Book id :{0}n" +
                        "Book name :{1}n" +
                        "Book price :{2}n" +
                        "Book Count :{3}", searchId.bookId, searchId.bookName, searchId.bookPrice, searchId.bookCount);
                    }
                }
            }
            else
            {
                Console.WriteLine("Book id {0} not found", find);
            }
        }
        //To borrow book details from the Library
        public static void Borrow()
        {
            Book book = new Book();
            BorrowDetails borrow = new BorrowDetails();
            Console.WriteLine("User id : {0}", (borrow.userId = borrowList.Count + 1));
            Console.Write("Name :");
            borrow.userName = Console.ReadLine();
            Console.Write("Book id :");
            borrow.borrowBookId = int.Parse(Console.ReadLine());
            Console.Write("Number of Books : ");
            borrow.borrowCount= int.Parse(Console.ReadLine());
            Console.Write("Address :");
            borrow.userAddress = Console.ReadLine();
            borrow.borrowDate = DateTime.Now;
            Console.WriteLine("Date - {0} and Time - {1}", borrow.borrowDate.ToShortDateString(), borrow.borrowDate.ToShortTimeString());
            if (bookList.Exists(x => x.bookId == borrow.borrowBookId))
            {
                foreach (Book searchId in bookList)
                {
                    if (searchId.bookCount >= searchId.bookCount - borrow.borrowCount && searchId.bookCount - borrow.borrowCount >= 0)
                    {
                        if (searchId.bookId == borrow.borrowBookId)
                        {
                            searchId.bookCount = searchId.bookCount - borrow.borrowCount;
                            break;
                        }
                    }
                    else
                    {
                        Console.WriteLine("Only {0} books are found", searchId.bookCount);
                        break;
                    }
                }
            }
            else
            {
                Console.WriteLine("Book id {0} not found", borrow.borrowBookId);
            }
            borrowList.Add(borrow);
        }
        //To return borrowed book to the library 
        public static void ReturnBook()
        {
            Book book = new Book();
            Console.WriteLine("Enter following details :");
            Console.Write("Book id : ");
            int returnId = int.Parse(Console.ReadLine());
            Console.Write("Number of Books:");
            int returnCount = int.Parse(Console.ReadLine());
            if (bookList.Exists(y => y.bookId == returnId))
            {
                foreach (Book addReturnBookCount in bookList)
                {
                    if (addReturnBookCount.x >= returnCount + addReturnBookCount.bookCount)
                    {
                        if (addReturnBookCount.bookId == returnId)
                        {
                            addReturnBookCount.bookCount = addReturnBookCount.bookCount + returnCount;
                            break;
                        }
                    }
                    else
                    {
                        Console.WriteLine("Count exists the actual count");
                        break;
                    }
                }
            }
            else
            {
                Console.WriteLine("Book id {0} not found", returnId);
            }
        }
    }
}

Answer 1

您应该通过使用bookId或更具体地使用对象的惟一Id来删除books。你张贴的代码是从列表中删除它使用的书的位置。拥有bookId的唯一目的是从任意数量的books中识别书，然后使用代码快速操作它。

让我告诉你一些关于面向对象编程(OOP)的东西，这将在某种程度上帮助你。每个对象都有三个特征:

在这里，标识符(像bookId这样的唯一的东西，可以用来选择它)是你应该用来操作对象(书籍)的东西，而不是对象的位置。

足够的理论，在你的代码

bookList.RemoveAt(Del - 1);

是罪魁祸首。在bookId的基础上改变它，你的问题就解决了。

谢谢

Answer 2

问题是，当您删除一本书时，您的图书列表将被重新排序，因此图书id不再反映您添加它们时的位置。例如，你的bookList有2本书(bookList[0]和bookList[1])。当您删除1本书时，您将留下booklist[0]，因此当您尝试删除下一本书时(您的代码显示您使用del -1来获取位置)，您将尝试从booklist[1]数组中删除，当然，booklist[1]不存在。

Answer 3

在您的代码中，您混淆了List和Array数据结构。让我们仔细看看:

if (bookList.Exists(x => x.bookId == Del))

在这里，您正在使用图书列表中的迭代搜索来查找一本书。首先，你可以通过引入额外的字典来做得更快，然后你的程序会更快。其次，在此之后，您将获得图书的id，并删除前一本图书，因为它不是列表，而是数组:

bookList.RemoveAt(Del - 1);

为什么不像预期的那样工作?这很简单，假设您已经添加了三本书，您的列表看起来像(这里的箭头是列表中书籍之间的链接):

1 --> 2 --> 3

删除第二本书后，列表如下:

1 --> 3

如果您添加另一本书，它的id将等于3 !因为这一行(bookList.Count在这里等于2):

Console.WriteLine("Book Id:{0}", book.bookId = bookList.Count + 1);

所以你的列表是这样的:

1 --> 3 --> 3

因此，您必须维护额外的计数器来惟一标识您的图书。另一件事是，你必须学习额外的LINQ方法，你可以使用，如RemoveAll方便地从列表中删除，Find方便地搜索到列表，等等。

Answer 4

问题是book id不稳定。它应该是唯一的列表，以确定正确的书。

这是一个快速解决方案。

在项目中添加Linq命名空间:

using System.Linq;

修改GetBook()方法，通过使用列表中的最大图书id号来生成唯一的bookId

var bookId = bookList.Count> 0 ? bookList.Max(b => b.bookId) : 0;
Console.WriteLine("Book Id:{0}", book.bookId = bookId + 1);