Class declaration syntax in C Sharp (C#) - Mini Project: Build & Apply

Class declaration syntax

📖 Scenario: You are creating a simple program to represent a book in a library system.

🎯 Goal: Build a class called Book with basic properties to hold book information.

📋 What You'll Learn

Create a class named Book

Add a public string property called Title

Add a public string property called Author

Add a public int property called Year

Create an instance of Book with specific values

Print the book details using the instance

💡 Why This Matters

🌍 Real World

Classes are used to model real-world objects in software, like books in a library system.

💼 Career

Understanding class declaration is fundamental for any C# developer to organize and structure code effectively.

1

Create the Book class

Write a class declaration named Book with no properties or methods yet.

C Sharp (C#)

// Your code here
// Declare a class named Book

Hint

Use the class keyword followed by the class name Book.

2

Add properties to the Book class

Inside the Book class, add three public properties: string Title, string Author, and int Year.

C Sharp (C#)

public class Book
{
    // Your code here
    // Add public properties Title, Author, and Year
}

Hint

Use auto-implemented properties with get; set;.

3

Create an instance of Book

Create a variable named myBook of type Book and set its Title to "The Great Gatsby", Author to "F. Scott Fitzgerald", and Year to 1925.

C Sharp (C#)

public class Book
{
    public string Title { get; set; }
    public string Author { get; set; }
    public int Year { get; set; }
}

// Create an instance of Book named myBook and set properties

Hint

Use object initializer syntax to set properties when creating myBook.

4

Print the book details

Write a Console.WriteLine statement to print the book details in the format: "Title: The Great Gatsby, Author: F. Scott Fitzgerald, Year: 1925" using the myBook instance.

C Sharp (C#)

public class Book
{
    public string Title { get; set; }
    public string Author { get; set; }
    public int Year { get; set; }
}

Book myBook = new Book
{
    Title = "The Great Gatsby",
    Author = "F. Scott Fitzgerald",
    Year = 1925
};

// Print the book details using Console.WriteLine

Hint

Use string interpolation with $"..." to include property values in the output.

Practice

1. What is the correct way to declare a class named Car in C#?

easy

A. Car class { }

B. class Car { }

C. class = Car { }

D. class: Car { }

Solution

1. Step 1: Understand class declaration syntax

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

2. Step 2: Match the correct syntax

   class Car { } uses class Car { }, which is the correct syntax for declaring a class named Car.

3. Final Answer:

   class Car { } -> Option B

4. Quick Check:

   Class declaration = class ClassName { } [OK]

Hint: Remember: class keyword + name + braces [OK]

Common Mistakes:

• Putting class name before keyword
• Using = or : instead of space
• Missing curly braces

2. Which of the following is a syntax error when declaring a class in C#?

easy

A. public class Person { }

B. class Animal { }

C. class 123Car { }

D. internal class House { }

Solution

1. Step 1: Check class name rules

   Class names must start with a letter or underscore, not a number.

2. Step 2: Identify invalid class name

   class 123Car { } uses class 123Car { }, which starts with digits, causing a syntax error.

3. Final Answer:

   class 123Car { } -> Option C

4. Quick Check:

   Class names cannot start with numbers [OK]

Hint: Class names must start with letter or underscore [OK]

Common Mistakes:

• Starting class name with a digit
• Using spaces in class name
• Using reserved keywords as class names

3. What will be the output of the following code?

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

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

medium

A. Buddy

B. Name

C. Dog

D. Compilation error

Solution

1. Step 1: Understand class field initialization

   The class Dog has a public field Name initialized to "Buddy".

2. Step 2: Trace the program output

   In Main, a Dog object is created and d.Name is printed, so output is "Buddy".

3. Final Answer:

   Buddy -> Option A

4. Quick Check:

   Field value printed = Buddy [OK]

Hint: Prints field value assigned in class [OK]

Common Mistakes:

• Confusing class name with field value
• Expecting method output instead of field
• Assuming compilation error without reason

4. Identify the error in this class declaration:

class Book
{
  string title;
  void SetTitle(string t)
  {
    title = t;
  }
}

medium

A. Missing access modifiers for field and method

B. Class name should be lowercase

C. Method SetTitle must return a value

D. Field title must be static

Solution

1. Step 1: Check access modifiers in class members

   By default, class members are private, but it's good practice to specify access modifiers explicitly.

2. Step 2: Identify missing access modifiers

   Field title and method SetTitle lack access modifiers like private or public, which can cause confusion or errors in some contexts.

3. Final Answer:

   Missing access modifiers for field and method -> Option A

4. Quick Check:

   Always specify access modifiers [OK]

Hint: Always add public/private to fields and methods [OK]

Common Mistakes:

• Assuming lowercase class names are required
• Thinking void methods must return a value
• Believing fields must be static

5. You want to create a class Student with a field name and a method GetName that returns the student's name. Which is the correct complete class declaration?

hard

A. class Student { public string name; public void GetName() { return name; } }

B. class Student { string name; string GetName() { name; } }

C. class Student { public string name; string GetName() { return name; } }

D. class Student { public string name; public string GetName() { return name; } }

Solution

1. Step 1: Check field and method access modifiers

   The field name and method GetName should be public to be accessible outside the class.

2. Step 2: Verify method return type and body

   GetName returns a string, so its return type must be string and it must return name.

3. Step 3: Identify correct option

   class Student { public string name; public string GetName() { return name; } } correctly declares name as public string and GetName as public string method returning name.

4. Final Answer:

   class Student { public string name; public string GetName() { return name; } } -> Option D

5. Quick Check:

   Public field + public string method returning field [OK]

Hint: Method return type must match returned value type [OK]

Common Mistakes:

• Missing return statement in method
• Wrong method return type (void instead of string)
• Missing public keyword for accessibility