Newb inheritance frustration

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I feel like I am doing everything right on this program but it is still spitting out errors. I am severely frustrated with this right now and I just need someone else to look at it.
I think the problem is something easy like a curley brace in the wrong place but I am getting a ton of errors.
I am just trying to learn about inheritance! I haven't been doing code long enough to properly debug this thing by myself and it's probably something simple like I said before, but I'm getting 40 errors for a simple program.

C#

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

namespace BookConsole
{
    class Program
    {
        static void Main()
        {
            public string input;
            Console.WriteLine("Do you want a book, a textbook, or a coffee table book?");
            string input = Console.ReadLine();

            if (input == "book") 
            {
                Book myBook = new Book();
                 
                Console.WriteLine("Enter Title");
                myBook.Title = Convert.ToString(Console.ReadLine());
                Console.WriteLine("Author?");
                myBook.Author = Convert.ToString(Console.ReadLine());
                Console.WriteLine("Enter price");
                myBook.Price = Convert.ToDouble(Console.ReadLine());
                Console.WriteLine("This is book {0} Titled: {1} Written by: {2} Price: {3}", myBook.BookNumber, myBook.Title, myBook.Author, myBook.Price);
            }
           else if (input == "textbook")
            {
                TextBook myText = new TextBook();
                Console.WriteLine("Enter Grade Level");
                myText.Grade = Convert.ToString(Console.ReadLine());
                Console.WriteLine("Enter Title");
                myText.Title = Convert.ToString(Console.ReadLine());
                Console.WriteLine("Author?");
                myText.Author = Convert.ToString(Console.ReadLine());
                Console.WriteLine("Enter price");
                myText.Price = Convert.ToDouble(Console.ReadLine());
                Console.WriteLine("This is book {0} Titled: {1} Written by: {2} Price: {3} Grade Level: {4}", myText.BookNumber, myText.Title, myText.Author, myText.Price, myText.Grade);
            }
            else 
            {
                CoffeeTableBook myCoffee = new CoffeeTableBook();
                 
                Console.WriteLine("Enter Title");
                myCoffee.Title = Convert.ToString(Console.ReadLine());
                Console.WriteLine("Author?");
                myCoffee.Author = Convert.ToString(Console.ReadLine());
                Console.WriteLine("Enter price");
                myCoffee.Price = Convert.ToDouble(Console.ReadLine());
                Console.WriteLine("This is book {0} Titled: {1} Written by: {2} Price: {3}", myCoffee.BookNumber, myCoffee.Title, myCoffee.Author, myCoffee.Price);
            }
    }
 }   
    static class Book
    {
        public double price;
        public int BookNumber { get; set; }
        public string Title { get; set; }
        public string Author { get; set; }
        public virtual double Price { get; set; }
    }
    static class TextBook : Book
    {
        public override double Price {
        get { return price; }
        set { 
           if (value < 20.00 || value > 80.00)
           { 
               Console.WriteLine("Invalid price.");
           }
           else
           {
               Console.WriteLine("Valid Price");
               price = value;
           }
        }
        }
        public char Grade { get; set; }
    }
    static class CoffeeTableBook : Book
    {
        public override double Price
        {
            get{ return price; }
            set{
                if (value < 35.00 || value > 100.00)
                {
                    Console.WriteLine("invalid Price.");
                }
                else
                {
                    Console.WriteLine("Valid Price");
                    price = value;
                }
            }
        }
    }
}

What I have tried:

Over the past 5 days I've tried changing places of curley brackets, adding and deleting them in different areas as well. I think my classes, inheritance and if-else statements are right. I made almost everything public out of frustration.

And I debugged to the best of my ability.

Posted 31-Mar-16 10:52am

Member 12370098

Updated 31-Mar-16 11:55am

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Sascha Lefèvre · Accepted Answer · 2016-03-31T11:18:00

You can't create instances of static classes:

C#

Book myBook = new Book();

-> Remove the static modifier from your three "book-classes".

Variables declared in methods can't have modifiers because they're automatically and always only visible within that method:

C#

public string input;

The advice would be to remove the public modifier from that variable declaration, but: You then re-declare input here:

C#

string input = Console.ReadLine();

-> Completely remove the first declaration of input.

TextBook.Grade is of type char, so you can't assign a string:

C#

myText.Grade = Convert.ToString(Console.ReadLine());

-> Proposed solution:

C#

string gradeInput = Console.ReadLine();
if (gradeInput.Length == 1)
{
   myText.Grade = gradeInput[0];
}
else
{
   // handle malformed input (e.g. error message, let user try again)
}

With these modifications all compiler errors should be dealt with.

Then there are some other issues which can be considered style/good practice issues:

- Don't validate values in property-setters. Alternatives: Either provide all values through the constructor, validate them there and in case of an invalid value, throw an exception. Or have a dedicated method for validation like:

C#

bool IsValid()
{
   // ...
}

(Which would, in an application where those books would subsequently be stored into a database, be called before the book would be stored and in case it's invalid, the saving-process would be stopped. So, in your case it would be a bit artificial.)

- Console.ReadLine() already returns a string. So passing it into Convert.ToString(..) is completely redundant:

C#

Convert.ToString(Console.ReadLine());

- For converting strings into other types, the preferred (static) methods are .Parse(..) or .TryParse(..) of the according types. The difference being that .Parse(..) returns the parsed value if successful and throws an exception if not successful while .TryParse(..) returns true if successful and places the parsed value into an out-parameter and returns false if not successful. The latter is often the more convenient option:

C#

double price;
if (!Double.TryParse(Console.ReadLine(), out price))
{
   // handle malformed input (e.g. error message, let user try again)
}

A free PDF-book on programming in C#: Introduction to Programming with C# / Java Books[^]

Sergey Alexandrovich Kryukov · Accepted Answer · 2016-03-31T11:24:00

What would you expect if you are not even trying to write in this language, C#?
And not even trying to understand very clear messages of a compiler. Apparently, you are falling in "frustration" well too early.

The trouble starts with this line:

C#

public string input;

What do you think it possibly could mean? This is a syntax of the declaration of the member of a class, a field. But you are placing it at the level of the implementation of the method Main. Methods don't have members, only types have. Removing "public" would fix it, by turning a member declaration into a variable.

This line screws up the rest of the code. From this point, there nothing to discuss. But on some line below you have

C#

static class TextBook : Book

What, did you fail to read that C# and .NET does not allow extension of static types? This is not a general rule of programming, but not allowed in .NET. This line screws up the whole class. And so on… I honestly explained first bug and don't need to go any further.

Fix it and proceed.

Now, I can see two possibilities: 1) you've don few random mistakes and failed to understand the compiler messages, due to low experience, 2) you have no idea of some very basic programming principles and no glue on how the language you are trying to use works. Second case seems more likely to me. Then you should start with having some manual on the language and platform, with explanation of general programming ideas, and read it all, without skipping a single line. You have to understand that you all you need is understanding; you don't have to memorize anything. But you should solve simple exercises to each chapter, better all of them, unless you feel some are too trivial. This way, most people managed to come to enlightenment, so you can, too.

I would add my simple rule: don't write a single line of code which you don't understand.

—SA

Newb inheritance frustration

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