Constructor overloading in C Sharp (C#) - Mini Project: Build & Apply

Constructor overloading

📖 Scenario: You are creating a simple program to represent a Book in a library system. Sometimes you know all details about the book, and sometimes you only know the title.

🎯 Goal: Build a Book class with two constructors: one that takes only the title, and another that takes title, author, and year. Then create two Book objects using these constructors and print their details.

📋 What You'll Learn

Create a class called Book with three fields: title, author, and year

Add a constructor that takes only string title and sets author to "Unknown" and year to 0

Add a constructor that takes string title, string author, and int year and sets all fields

Create two Book objects: one using the single-parameter constructor and one using the three-parameter constructor

Print the details of both books in the format: Title: {title}, Author: {author}, Year: {year}

💡 Why This Matters

🌍 Real World

Constructor overloading helps create flexible classes that can be initialized with different sets of information, like creating user profiles with varying details.

💼 Career

Understanding constructor overloading is important for software developers to write clean, reusable, and flexible code in object-oriented programming.

1

Create the Book class with fields

Create a class called Book with three public fields: string title, string author, and int year.

C Sharp (C#)

public class Book
{
    // Your code here
}

Hint

Use public string title; to declare the fields inside the class.

2

Add two constructors to the Book class

Add two constructors inside the Book class: one that takes string title and sets author to "Unknown" and year to 0, and another that takes string title, string author, and int year and sets all fields.

C Sharp (C#)

public class Book
{
    public string title;
    public string author;
    public int year;

    // Your code here
}

Hint

Use this.title = title; inside each constructor to set the fields.

3

Create two Book objects using both constructors

In the Main method, create two Book objects: book1 using the constructor with only title "C# Basics", and book2 using the constructor with title "Advanced C#", author "John Doe", and year 2023.

C Sharp (C#)

public class Book
{
    public string title;
    public string author;
    public int year;

    public Book(string title)
    {
        this.title = title;
        this.author = "Unknown";
        this.year = 0;
    }

    public Book(string title, string author, int year)
    {
        this.title = title;
        this.author = author;
        this.year = year;
    }
}

class Program
{
    static void Main()
    {
        // Create book1 and book2 here
    }
}

Hint

Use new Book("C# Basics") to create book1.

4

Print the details of both books

Add Console.WriteLine statements to print the details of book1 and book2 in the format: Title: {title}, Author: {author}, Year: {year}.

C Sharp (C#)

public class Book
{
    public string title;
    public string author;
    public int year;

    public Book(string title)
    {
        this.title = title;
        this.author = "Unknown";
        this.year = 0;
    }

    public Book(string title, string author, int year)
    {
        this.title = title;
        this.author = author;
        this.year = year;
    }
}

class Program
{
    static void Main()
    {
        Book book1 = new Book("C# Basics");
        Book book2 = new Book("Advanced C#", "John Doe", 2023);

        // Print book details here
    }
}

Hint

Use Console.WriteLine($"Title: {book1.title}, Author: {book1.author}, Year: {book1.year}"); to print details.

Practice

1. What does constructor overloading in C# allow you to do?

easy

A. Override methods with the same name

B. Create multiple constructors with different parameter lists in the same class

C. Use constructors without parameters only

D. Create only one constructor per class

Solution

1. Step 1: Understand constructor overloading concept

   Constructor overloading means having more than one constructor in a class, each with a different set of parameters.

2. Step 2: Identify what overloading allows

   This allows creating objects in different ways depending on the parameters passed.

3. Final Answer:

   Create multiple constructors with different parameter lists in the same class -> Option B

4. Quick Check:

   Constructor overloading = multiple constructors with different parameters [OK]

Hint: Multiple constructors differ by parameter list only [OK]

Common Mistakes:

• Thinking only one constructor is allowed
• Confusing overloading with overriding
• Believing constructors must have no parameters

2. Which of the following is a correct constructor overloading syntax in C#?

easy

A. public class Car { public Car() {} public Car(string model) {} }

B. public class Car { public void Car() {} public void Car(string model) {} }

C. public class Car { public Car() {} public Car() {} }

D. public class Car { Car() {} Car() {} }

Solution

1. Step 1: Check constructor syntax

   Constructors must have the same name as the class and no return type.

2. Step 2: Identify correct overloading

   public class Car { public Car() {} public Car(string model) {} } has two constructors with different parameters and correct syntax.

3. Final Answer:

   public class Car { public Car() {} public Car(string model) {} } -> Option A

4. Quick Check:

   Constructor syntax correct and overloaded by parameters [OK]

Hint: Constructors have no return type and match class name [OK]

Common Mistakes:

• Adding return type to constructors
• Defining multiple constructors with same parameters
• Omitting access modifier (not mandatory but common style)

3. What will be the output of this code?

class Box {
  public int length;
  public Box() { length = 5; }
  public Box(int l) { length = l; }
}
class Program {
  static void Main() {
    Box b1 = new Box();
    Box b2 = new Box(10);
    Console.WriteLine(b1.length + ", " + b2.length);
  }
}

medium

A. 5, 10

B. 0, 10

C. 5, 5

D. 10, 10

Solution

1. Step 1: Analyze constructors called

   b1 uses the parameterless constructor setting length = 5; b2 uses the constructor with int parameter setting length = 10.

2. Step 2: Determine printed values

   Console.WriteLine prints b1.length (5) and b2.length (10) separated by a comma.

3. Final Answer:

   5, 10 -> Option A

4. Quick Check:

   Default constructor sets 5, parameterized sets 10 [OK]

Hint: Check which constructor is called for each object [OK]

Common Mistakes:

• Assuming default int value 0 instead of assigned 5
• Confusing which constructor runs for each object
• Mixing up output order

4. Identify the error in this constructor overloading code:

class Person {
  public string name;
  public Person(string n) { name = n; }
  public Person(string n) { name = n.ToUpper(); }
}

medium

A. Constructor name does not match class name

B. Missing return type in constructors

C. Duplicate constructor with same parameter list

D. Cannot assign string to name

Solution

1. Step 1: Check constructor parameter lists

   Both constructors have the same parameter type and count (string n), causing duplication.

2. Step 2: Understand overloading rules

   Constructors must differ by parameter types or count to overload; identical signatures cause error.

3. Final Answer:

   Duplicate constructor with same parameter list -> Option C

4. Quick Check:

   Same parameters = duplicate constructor error [OK]

Hint: Constructor signatures must differ by parameters [OK]

Common Mistakes:

• Thinking constructors can differ by body only
• Adding return type mistakenly
• Ignoring parameter list uniqueness

5. You want to create a class Rectangle with overloaded constructors:
- One constructor takes no parameters and sets width and height to 1.
- Another takes one parameter and sets both width and height to that value.
- Another takes two parameters to set width and height separately.
Which of these constructor definitions correctly implements this?

hard

A. public Rectangle() { width = 1; height = 1; } public Rectangle(int w, int h) { width = w; height = h; } public Rectangle(int w, int h) { width = w; height = h; }

B. public Rectangle() { width = 1; height = 1; } public Rectangle(int size) { width = size; height = size; } public Rectangle(int size) { width = size; height = size; }

C. public Rectangle(int w, int h) { width = w; height = h; } public Rectangle() { width = 1; height = 1; } public Rectangle(int size) { width = size; }

D. public Rectangle() { width = 1; height = 1; } public Rectangle(int size) { width = size; height = size; } public Rectangle(int w, int h) { width = w; height = h; }

Solution

1. Step 1: Check parameter lists for uniqueness

   public Rectangle() { width = 1; height = 1; } public Rectangle(int size) { width = size; height = size; } public Rectangle(int w, int h) { width = w; height = h; } has three constructors with distinct parameter lists: no parameters, one int, and two ints.

2. Step 2: Verify each constructor sets values correctly

   Each constructor sets width and height as required: default 1, same size, or separate sizes.

3. Final Answer:

   public Rectangle() { width = 1; height = 1; } public Rectangle(int size) { width = size; height = size; } public Rectangle(int w, int h) { width = w; height = h; } -> Option D

4. Quick Check:

   Distinct parameter lists and correct assignments [OK]

Hint: Each constructor must have unique parameter count or types [OK]

Common Mistakes:

• Defining two constructors with same parameter types
• Mixing order of constructors causing confusion
• Not setting default values in parameterless constructor