C#

public class Book
    {
        public String BookName { get; set; }
        public String AuthorName { get; set; }
        public int NumberOfCopiesInStock { get; set; }
        public String ISBN { get; set; }

        public Book(String bookName, String authorName, int numberOfCopiesInStock, String isbn)
        {
            this.BookName = bookName;
            this.AuthorName = authorName;
            this.NumberOfCopiesInStock = numberOfCopiesInStock;
            this.ISBN = isbn;
        }

        public override String ToString()
        {
            return ("BookName: " + BookName
                  + "\n"
                  + "Author Name: " + AuthorName
                  + "\n"
                  + "Number Of Copies: " + NumberOfCopiesInStock
                  + "\n"
                  + "ISBN: " + ISBN);
        }
    }

public class Search
    {
        public Boolean SearchForBook()
        {
            Console.WriteLine("Please enter name of book: ");
            String search = Console.ReadLine();
            UserInput.MakeTheComputerSleep();
            foreach (Book b in UserInput.bookList)
            {
                if (b.BookName.Equals(search))
                {
                    Console.WriteLine(b);
                    return true;
                }
            }
            Console.WriteLine("Book doesn't exist! ");
            return false;
        }
    }

<pre>public class UserInput
    {
        public static Boolean KeepGoing = true;
        public static List<Book> bookList = new List<Book>();
        private static readonly String INPUT_ERROR_MESSAGE = "Please only enter NUMBERS!";
        private static readonly String INVALID_CHOICE = "INVALID CHOICE ENTERED!";
        private static readonly String SEARCH_MESSAGE = "Searching for book,please wait......";
        private static Random RandomObject = new Random();

        public static void WelcomeMessage()
        {
            Console.WriteLine("********************");
            Console.WriteLine("*       Cork       *");
            Console.WriteLine("*      Library     *");
            Console.WriteLine("********************");
        }

        private static void MenuHeader()
        {
            Console.WriteLine("********************");
            Console.WriteLine("*       Menu       *");
            Console.WriteLine("*      Options     *");
            Console.WriteLine("********************");
        }

        private static void MenuOptions()
        {
            Console.WriteLine("1.) Add Book.             ");
            Console.WriteLine("2.) Search for Book.      ");
            Console.WriteLine("3.) Delete Book.          ");
            Console.WriteLine("4.) Display all Book.     ");
            Console.WriteLine("0.) Exit.                 ");
        }

        public static void GetUserInput()
        {
            int choice;
            MenuHeader();
            do
            {
                MenuOptions();
                Console.WriteLine(">");
                choice = 0;
                while (!int.TryParse(Console.ReadLine(), out choice))
                {
                    Console.WriteLine(INPUT_ERROR_MESSAGE);
                }
                PickChoice(choice);
            } while (choice != 0);
        }

        private static void PickChoice(int choice)
        {
            switch (choice)
            {
                case 1:
                    AddBook addBook = new AddBook();
                    addBook.EnterBookInfo();
                    break;

                case 2:
                    Search search = new Search();
                    search.SearchForBook();
                    break;

                case 3:
                    break;

                case 4:
                    
                    AddBook addBook1 = new AddBook();
                    addBook1.PrintListOfBooks();
                    break;

                case 0:
                    Exit exit = new Exit();
                    exit.Exit_Application();
                    break;

                default:
                    Console.WriteLine(INVALID_CHOICE);
                    break;
            }
        }

        public static void MakeTheComputerSleep()
        {
            int number = RandomObject.Next(10) + 1;
            Console.WriteLine("Searching for Book.......");
            Thread.Sleep(number * 1000);
        }

        
    }

public class AddBook
    {
        public void EnterBookInfo()
        {
            while (UserInput.KeepGoing)
            {

                Console.WriteLine("Please enter name of book: ");
                String BookName = Console.ReadLine();

                if (BookName.Equals("end"))
                {
                    break;
                }

                Console.WriteLine("Please enter Author Name: ");
                String AuthorName = Console.ReadLine();

                Console.WriteLine("Please enter ISBN Number: ");
                String ISBN = Console.ReadLine();

                Console.WriteLine("Please enter number of books: ");
                int NumberOfCopiesInStock = Convert.ToInt32(Console.ReadLine());

                Book book1 = new Book("Neverwhere", "Neil Gaimen", 1, "aaaaa");
                Book book = new Book(BookName, AuthorName, NumberOfCopiesInStock, ISBN);
                UserInput.bookList.Add(book);
                UserInput.bookList.Add(book1);

            }

        }

        public void PrintListOfBooks()
        {
            foreach (Book b in UserInput.bookList)
            {
                Console.WriteLine(b.ToString());
                Console.WriteLine();
            }
        }
    }

class Program
    {
        public static void Main(string[] args)
        {
            UserInput.WelcomeMessage();
            UserInput.GetUserInput();
        }
    }

int cellvalue3 = int.Parse(my_table3.Rows[i][19].ToString());

System.FormatException: 'Input string was not in a correct format.'

namespace laptopWatcher {  
  public partial class clockCountDown: Window {  
    public string theCntDownTimerTime = "";  
  
    public clockCountDown() {  
      InitializeComponent();  
      //get countdown time  
      theCntDownTimerTime = getTimeToStart();  
    }  
  
    private void Window_Loaded(object sender, RoutedEventArgs e) {  
      var desktopWorkingArea = SystemParameters.WorkArea;  
      this.Left = desktopWorkingArea.Right - this.Width - 20;  
      this.Top = desktopWorkingArea.Top + this.Height - 30;  
      var ts = ((60 - DateTime.Now.Second) * 1000 - DateTime.Now.Millisecond);  
  
      clockTimer.Tick += new EventHandler(clockTimer_tick);  
      clockTimer.Interval = new TimeSpan(0, 0, 35);  
      clockTimer.Start();  
  
      //Populate the time once to show to user  
      bgTxt.Text = DateTime.Now.ToString("h:mm tt");  
      txt.Text = DateTime.Now.ToString("h:mm tt");  
  
      //check if time for count down  
      if (txt.Text.ToLower().Equals(theCntDownTimerTime.ToLower())) {  
        _timer.Stop();  
        TimeSpan time = TimeSpan.Parse(theCntDownTimerTime);  
        cdownTimer((_time).TotalSeconds);  
      }  
  
      _tws = new TinyWS();  
      Thread t = new Thread(new ThreadStart(_tws.startWS));  
  
      t.Start();  
    }  
  
    private void clockTimer_tick(object sender, EventArgs e) {  
      bgTxt.Text = DateTime.Now.ToString("h:mm tt");  
      txt.Text = DateTime.Now.ToString("h:mm tt");  
      Console.WriteLine(txt.Text.ToLower() + " vs " + theCntDownTimerTime.ToLower());  
    }  
  
    public string getTimeToStart() {  
      string line;  
  
      using(StreamReader sr = new StreamReader(Environment.CurrentDirectory + "\\timestart.txt")) {  
        line = sr.ReadLine();  
      }  
  
      return line.ToLower();  
    }  
  
    // etc etc....  
  }  
}

namespace laptopLogin {  
  class TinyWS: clockCountDown {  
    HttpListener listener = new HttpListener();  
    clockCountDown ccd = new clockCountDown();  
  
    public class receivedData {  
      public string changeCNT {  
        get;  
        set;  
      }  
      public int timeAdd {  
        get;  
        set;  
      }  
      public bool internet {  
        get;  
        set;  
      }  
      public bool shutdownNow {  
        get;  
        set;  
      }  
    }  
  
    public void startWS() {  
      var prefixes = new List < string > () {  
        "http://*:8888/"  
      };  
  
      foreach(string s in prefixes) {  
        listener.Prefixes.Add(s);  
      }  
  
      listener.Start();  
      Console.WriteLine("Listening...");  
  
      while (true) {  
        HttpListenerContext context = listener.GetContext();  
        HttpListenerRequest request = context.Request;  
  
        string documentContents;  
  
        using(Stream receiveStream = request.InputStream) {  
          using(StreamReader readStream = new StreamReader(receiveStream, Encoding.UTF8)) {  
            documentContents = readStream.ReadToEnd();  
          }  
        }  
  
        Console.WriteLine($"Recived request for {request.Url}");  
        Console.WriteLine(documentContents);  
        HttpListenerResponse response = context.Response;  
  
        //Check out the response  
        receivedData jsonSent = JsonConvert.DeserializeObject < receivedData > (documentContents);  
  
        if (jsonSent.changeCNT.ToLower() != ccd.getTimeToStart()) {  
          //The default shutdown time has changed so update the txt file.  
          using(StreamWriter sw = new StreamWriter(Environment.CurrentDirectory + "\\timestart.txt", false)) {  
            sw.WriteLine(jsonSent.changeCNT);  
          }  
  
          ccd.theCntDownTimerTime = jsonSent.changeCNT;  
        }  
  
        //Reply  
        string responseString = "hit";  
        byte[] buffer = System.Text.Encoding.UTF8.GetBytes(responseString);  
        response.ContentLength64 = buffer.Length;  
        Stream output = response.OutputStream;  
        output.Write(buffer, 0, buffer.Length);  
        output.Close();  
      }  
    }  
  
    public void stopWS() {  
      listener.Stop();  
    }  
  }  
}  

public string theCntDownTimerTime = "";  
public string _newCNT {  
  get {  
    return theCntDownTimerTime;  
  }  z
  set {  
    theCntDownTimerTime = value;  
  }  
}