Question

The program works in its current for but I would like to make it more object oriented like its design using constructors and such but I don’t know where to start and how to make it work. I would like your insight and examples on how you would accomplish this task? Here is a sample UML for what I am trying to do.

Original Design

  public static class IsbnConsole
{
   public static void Main(string[] args)
    {
        Console.Write("Enter a valid 10 digit ISBN Number ");
        string isbn = checkIsbnClass.DestabilizeIsbn(Console.ReadLine()); // Normalizes the input and puts it on string "str"
        if (isbn.Length > 10 || isbn.Length < 9) // If the string length is greather than 10, or smaller than 9
        {
            Console.WriteLine("The number you have entered is not a valid ISBN try again."); // Print invalid number
            Console.ReadLine();
        }
        else if (isbn.Length == 10) // If the length is 10
        {
            if (checkIsbnClass.CheckNumber(isbn)) // If function CheckNum return "true"...
                Console.WriteLine("The number you have entered is a Valid ISBN");

            else // If it returns "false"...
                Console.WriteLine("The number you have entered is not a valid ISBN try again.");
                Console.ReadLine();
        }
        else // Else (If the number is NOT greater than 10 or smaller than 9, NOR is it 10 -> If the number is 9)
        {
            Console.WriteLine("The Check digit that corresponds to this ISBN number is " + checkIsbnClass.CheckIsbn(isbn) + "."); // Print the checksum digit
            Console.ReadLine();
        }

  public static class checkIsbnClass
{ 

public static string CheckIsbn(string isbn) // Calculates the 10th digit of a 9-digits partial ISBN number
    {
        int sum = 0;
        for (int i = 0; i < 9; i++) // For each number...
        {
            sum += int.Parse(isbn[i].ToString()) * (i + 1); // ...Multiply the number by it's location in the string
        }
        if ((sum % 11) == 10) // If the remainder equals to 10...
        {
            return "x"; // Output X
        }
        else // If it does not equal to 10...
        {
            return (sum % 11).ToString(); // Output the number
        }
    }
  public static bool CheckNumber(string isbn) // Checks if the checksum digit is correct
    {
        if (isbn[9].ToString() == CheckIsbn(isbn)) // If the 10th digit of the number is the same as the calculated digit...
            return true;
        else // If they're not the same...
            return false;
    }
  public static string DestabilizeIsbn(string isbn) // replace the string
  {
      return isbn.Replace("-", "").Replace(" ", "");
  }

Newly Designed Method Using Constructors

   public class isbn
    {   //attributes
         private string isbnNum;
         //method   
         public string GetIsbn()
         {
             return this.isbnNum;
         }
           //constructor
           public isbn()
           {
               Console.Write("Enter Your ISBN Number: ");
               this.isbnNum = Console.ReadLine();

           }//end default constructor

            //method
           public string displayISBN()
           {

               return  this.GetIsbn();

           }


       public static void Main(string[] args)
        {
            //create a new instance of the ISBN/book class

            isbn myFavoriteBook = new isbn();

            //contains the method for checking validity 
            bool isValid = CheckDigit.CheckIsbn(myFavoriteBook.GetIsbn());

            //print out the results of the validity.
            Console.WriteLine(string.Format("Your book {0} a valid ISBN",
                                       isValid ? "has" : "doesn't have"));

            Console.ReadLine();

        }

public static class CheckDigit
{       // attributes
    public static string NormalizeIsbn(string isbn)
    {
        return isbn.Replace("-", "").Replace(" ", "");
    }
   public static bool CheckIsbn(string isbn) // formula to check ISBN's validity
    {
        if (isbn == null)
            return false;

        isbn = NormalizeIsbn (isbn);
        if (isbn.Length != 10)
            return false;

        int result;
        for (int i = 0; i < 9; i++)
            if (!int.TryParse(isbn[i].ToString(), out result))
                return false;

        int sum = 0;
        for (int i = 0; i < 9; i++)
            sum += (i + 1) * int.Parse(isbn[i].ToString());

        int remainder = sum % 11;
        if (remainder == 10)
            return isbn[9] == 'X';
        else
            return isbn[9] == (char)('0' + remainder);
    }

Answer 1

public static class IsbnConsole 
{ 
   public static void Main(string[] args) 
    { 
        Console.Write("Enter a valid 10 digit ISBN Number "); 
        string isbn = checkIsbnClass.DestabilizeIsbn(Console.ReadLine()); // Normalizes the input and puts it on string "str" 

        Isbn isbn = new Isbn(Console.In)
        if (!isbn.CheckLength())   
            Console.WriteLine("The number you have entered is not a valid ISBN try again."); // Print invalid number 
        } 
        else if (isbn.HasCheckDigit)
        { 
            if (isbn.CheckNumber(isbn)) 
                Console.WriteLine("The number you have entered is a Valid ISBN"); 
            else
                Console.WriteLine("The number you have entered is not a valid ISBN try again."); // Print invalid number 
        } 
        else 
        { 
            Console.WriteLine("The Check digit that corresponds to this ISBN number is " + isbn.GetCheckDigit(isbn) + "."); // Print the checksum digit 
        } 
        Console.ReadLine(); 
}

public class Isbn
{
   public Isbn(TextReader cin)
   {
        /// do stuff here.
   }

   public bool CheckLength()
   {
        /// do stuff here.
   }

   public bool HasCheckDigit {  get {    ..... } }
   public int  GetCheckDigit() {..... }
   public bool CheckNumber() {......}
}