Why classes are needed in C Sharp (C#) - See It in Action

Why Classes Are Needed

📖 Scenario: Imagine you are organizing a library. You want to keep track of books with their title, author, and number of pages. Instead of writing separate variables for each book, you can use a class to group all this information together.

🎯 Goal: You will create a simple Book class to hold information about a book. Then, you will create an object of this class and display its details.

📋 What You'll Learn

Create a class named Book with three public fields: Title, Author, and Pages.

Create an object of the Book class named myBook.

Assign the values "The Great Gatsby" to Title, "F. Scott Fitzgerald" to Author, and 180 to Pages.

Print the book details in the format: Title: The Great Gatsby, Author: F. Scott Fitzgerald, Pages: 180.

💡 Why This Matters

🌍 Real World

Classes are used everywhere in software to model real-world things like books, cars, or users, making programs easier to build and understand.

💼 Career

Understanding classes is essential for any software developer because they form the foundation of object-oriented programming, which is widely used in industry.

1

Create the Book class

Create a public class called Book with three public fields: string Title, string Author, and int Pages.

C Sharp (C#)

// Your code here

Hint

Think of a class as a blueprint. Here, Book is the blueprint with fields to hold information.

2

Create a Book object and assign values

Create an object named myBook of type Book. Assign "The Great Gatsby" to myBook.Title, "F. Scott Fitzgerald" to myBook.Author, and 180 to myBook.Pages.

C Sharp (C#)

public class Book
{
    public string Title;
    public string Author;
    public int Pages;
}

// Your code here

Hint

Use new Book() to create the object, then set each field using the dot . operator.

3

Write code to display the book details

Write a Console.WriteLine statement to print the book details in this exact format: Title: The Great Gatsby, Author: F. Scott Fitzgerald, Pages: 180 using myBook fields.

C Sharp (C#)

public class Book
{
    public string Title;
    public string Author;
    public int Pages;
}

Book myBook = new Book();
myBook.Title = "The Great Gatsby";
myBook.Author = "F. Scott Fitzgerald";
myBook.Pages = 180;

// Your code here

Hint

Use string interpolation with $"...{variable}..." to insert values inside the string.

4

Run the program to see the output

Run the program and observe the output. It should exactly print: Title: The Great Gatsby, Author: F. Scott Fitzgerald, Pages: 180

C Sharp (C#)

using System;

public class Book
{
    public string Title;
    public string Author;
    public int Pages;
}

class Program
{
    static void Main()
    {
        Book myBook = new Book();
        myBook.Title = "The Great Gatsby";
        myBook.Author = "F. Scott Fitzgerald";
        myBook.Pages = 180;

        // Your code here
    }
}

Hint

Make sure your output matches exactly, including commas and spaces.

Practice

1. Why do we use classes in C# programming?

easy

A. To make the program run slower

B. To write code faster without any structure

C. To avoid using variables

D. To group related data and actions together

Solution

1. Step 1: Understand the purpose of classes

   Classes help organize data (variables) and actions (methods) that belong together.

2. Step 2: Compare options with class purpose

   Only grouping related data and actions matches the main reason for classes.

3. Final Answer:

   To group related data and actions together -> Option D

4. Quick Check:

   Classes group data and actions [OK]

Hint: Classes bundle data and behavior in one place [OK]

Common Mistakes:

• Thinking classes slow down programs
• Believing classes are only for speed
• Confusing classes with variables

2. Which of the following is the correct way to declare a simple class named Car in C#?

easy

A. class Car { }

B. Car class { }

C. class = Car { }

D. class Car() { }

Solution

1. Step 1: Recall C# class declaration syntax

   In C#, a class is declared using the keyword class followed by the class name and curly braces.

2. Step 2: Check each option

   class Car { } matches the correct syntax: class Car { }. Others have syntax errors.

3. Final Answer:

   class Car { } -> Option A

4. Quick Check:

   Correct class syntax [OK]

Hint: Use 'class ClassName { }' to declare classes [OK]

Common Mistakes:

• Putting parentheses after class name
• Swapping 'class' and class name
• Using '=' sign in declaration

3. What will be the output of this C# code?

class Dog {
  public string Name = "Buddy";
}

class Program {
  static void Main() {
    Dog myDog = new Dog();
    Console.WriteLine(myDog.Name);
  }
}

medium

A. Buddy

B. myDog

C. Dog

D. Name

Solution

1. Step 1: Understand object creation and field access

   The code creates a new Dog object and accesses its Name field which is set to "Buddy".

2. Step 2: Determine what is printed

   The Console.WriteLine prints the value of myDog.Name, which is "Buddy".

3. Final Answer:

   Buddy -> Option A

4. Quick Check:

   Object field value printed = Buddy [OK]

Hint: Object.field prints the stored value [OK]

Common Mistakes:

• Printing the object name instead of field
• Confusing class name with field value
• Expecting variable name as output

4. Identify the error in this class definition:

class Person {
  string name;
  void SetName(string newName) {
    name = newName;
  }
}

class Program {
  static void Main() {
    Person p = new Person();
    p.SetName("Alice");
  }
}

medium

A. Class Person must inherit from another class

B. Field name should be static

C. Method SetName must be public to be accessible

D. Cannot create object of class Person

Solution

1. Step 1: Check method accessibility

   The method SetName has no access modifier, so it is private by default and not accessible outside the class.

2. Step 2: Understand object method call

   In Main, p.SetName("Alice") tries to call a private method, causing an error.

3. Final Answer:

   Method SetName must be public to be accessible -> Option C

4. Quick Check:

   Private method can't be called outside class [OK]

Hint: Make methods public to call them from outside [OK]

Common Mistakes:

• Assuming methods are public by default
• Thinking fields must be static
• Believing inheritance is mandatory

5. You want to model a Book with a title and author, and a method to display its info. Why is using a class better than separate variables?

hard

A. Separate variables run faster and use less memory

B. Classes keep related data and behavior together, making code reusable and clear

C. Classes make code longer and harder to read

D. Using separate variables avoids the need for methods

Solution

1. Step 1: Understand the benefit of grouping data and methods

   A class groups the book's title, author, and display method, making the code organized and reusable.

2. Step 2: Compare with separate variables

   Separate variables scatter data and methods, making code harder to maintain and reuse.

3. Final Answer:

   Classes keep related data and behavior together, making code reusable and clear -> Option B

4. Quick Check:

   Classes improve organization and reuse [OK]

Hint: Group data and actions in classes for clarity [OK]

Common Mistakes:

• Thinking classes slow down programs
• Believing separate variables are always better
• Ignoring benefits of code reuse