图书馆管理系统。借书布尔值

Question

所以我目前正在尝试以初学者的身份掌握 c#，我正在构建一个图书馆管理系统。我已经添加了我需要的一切，但是，我想添加它的一个功能特性，你可以借一本书，它会将它标记为已借，并且在他们归还之前没有其他人能够借出它。我尝试为它添加一个布尔值来将一本书标记为已借，但它似乎并没有将一本书标记为已借，而是让我无限次运行借阅功能。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.IO;

namespace Bibliotek
{
    //Definerar klassen Book
    class Book
    {
        public boolean IsBorrowed
        { get; set; }
        public string Author
        { get; set; }
        public string Title
        { get; set; }

    }
    class Program
    {
        static List<Book> BookList = new List<Book>();
        static Book Book = new Book();


        //Menyn och startsidan till programmet
        static void Main(string[] args)
        {
            using (StreamReader readFile = new StreamReader("Bookfil.txt"))
            {
                string s;
                while ((s = readFile.ReadLine()) != null)
                {
                    Book Book = new Book();
                    string[] BookData = s.Split(',');
                    Book.Author = BookData[0];
                    Book.Title = BookData[1];
                    BookList.Add(Book);
                }
                readFile.Close();
            }
 bool stäng = true;
                while (stäng)
                {
                    Console.WriteLine("\n\nVälkommen till biblioteket!\n" +
                    "\n1)Lägg till Bok\n" +
                    "2)Radera Bok\n" +
                    "3)Leta efter Bok\n" +
                    "4)Låna Bok\n" +
                    "5)Lämna tillbaks Bok\n" +
                    "6)Stäng program\n\n");

                    int val = int.Parse(Console.ReadLine());

                    if (val == 1)
                    {
                        AddBook();
                    }
                    else if (val == 2)
                    {
                        RemoveBook();
                    }
                    else if (val == 3)
                    {
                        SearchBook();
                    }
                    else if (val == 4)
                    {
                        BorrowBook();
                    }
                    else if (val == 5)
                    {
                        ReturnBook();
                    }
                    else if (val == 6)
                    {
                        Console.WriteLine("Tack!");
                        stäng = false;
                        break;
                    }
                    else
                    {
                        Console.WriteLine("Invalid option\nFörsök igen! ");
                    }
                }

        public static void BorrowBook()
        {
            Console.Write("Mata in en Author eller Booktitel: ");
            string borrow = Console.ReadLine();
            foreach (Book b in BookList)
            {
                if (b.Title.Equals(borrow))
                {
                    if (b.IsBorrowed == true)
                    {
                        Console.WriteLine("Book is already taken");
                    }
                    else
                    {
                        Console.WriteLine(b.Author + ":" + b.Title);
                        b.IsBorrowed = true;
                    }
                }

            }
        }