Complete OOP Concepts Using C++ to Crack Any Interview with Code and Real-time Examples

6 min readJul 31, 2023

Introduction

In the world of software development, mastering Object-Oriented Programming (OOP) concepts is essential for excelling in interviews and building robust applications. C++ is a powerful programming language that fully supports OOP principles, making it a popular choice for interview assessments. This article will delve into the fundamental OOP concepts in C++, providing you with comprehensive knowledge and real-time examples to ace your interviews confidently.

What is Object-Oriented Programming (OOP)?
The Four Pillars of OOP

Encapsulation
Inheritance
Polymorphism
Abstraction

Classes and Objects in C++

Creating Classes
Defining Class Members
Constructors and Destructors
Creating Objects

Access Modifiers

Public Access Modifier
Private Access Modifier
Protected Access Modifier

Inheritance in C++

Single Inheritance
Multiple Inheritance
Multilevel Inheritance

Polymorphism in C++

Function Overloading
Operator Overloading
Virtual Functions

Abstraction and Interfaces

Abstract Classes
Pure Virtual Functions
Interfaces in C++

Static Members

Static Data Members
Static Member Functions

C++ Standard Template Library (STL)

Containers
Iterators
Algorithms

Real-time Examples of OOP in C++

Building a Banking System
Developing a Game Engine
Creating a Shapes Hierarchy

Best Practices and Tips for OOP Interviews

Understand the Problem Statement
Demonstrate Modularity and Reusability
Handle Exceptional Cases
Use Standard Library Features

Common Interview Questions on C++ OOP

Difference between Encapsulation and Abstraction
Why is Polymorphism Important?
Explain Virtual Functions and Pure Virtual Functions
How to Achieve Multiple Inheritance in C++?

Conclusion

What is Object-Oriented Programming (OOP)?

Object-Oriented Programming is a programming paradigm that focuses on designing software using objects and classes. It emphasizes data encapsulation, inheritance, polymorphism, and abstraction to model real-world entities and interactions efficiently. OOP promotes code reusability, modularity, and easier maintenance, making it widely adopted in software development.

The Four Pillars of OOP

Encapsulation

Encapsulation is the process of bundling data and methods together in a class, restricting direct access to the internal state of objects. It ensures data security and promotes a clear separation of concerns.

Inheritance

Inheritance allows a class to inherit properties and behaviors from another class. It facilitates code reuse and enables the creation of a hierarchy of classes.

Polymorphism

Polymorphism allows objects to be treated as instances of their parent class. It simplifies code and enables flexible behavior based on the object’s specific type.

Abstraction

Abstraction involves hiding complex implementation details and providing a simplified interface. It helps manage complexity and enhances code understandability.

Classes and Objects in C++

Creating Classes

class Person {
// class members
};

In C++, a class is defined using the class keyword, followed by the class name and a set of curly braces. For example:

class Person {
    // class members
};

Defining Class Members

Class members include data members (variables) and member functions (methods). Data members represent the state of the object, while member functions define its behavior.

Constructors and Destructors

Constructors are special member functions that initialize objects when they are created, while destructors clean up resources when objects are destroyed.

Creating Objects

Objects are instances of classes. They are created using the class name followed by parentheses. For example:

cppCopy code

Person john; // Creating an object of the Person class

Access Modifiers

C++ provides three access modifiers: public, private, and protected. These determine the visibility of class members.

Public Access Modifier

Public members are accessible from any part of the program. They define the interface of the class.

Private Access Modifier

Private members can only be accessed within the class itself. They hide the implementation details from the outside world.

Protected Access Modifier

Protected members are accessible within the class and its derived classes. They allow for controlled access in inheritance.

Inheritance in C++

In C++, inheritance is a powerful feature that enables one class to inherit properties and behaviors from another class.

Single Inheritance

In single inheritance, a class can inherit from only one base class.

Multiple Inheritance

Multiple inheritance allows a class to inherit from multiple base classes.

Multilevel Inheritance

In multilevel inheritance, a class derives from another class, which in turn is derived from a base class.

Polymorphism in C++

Polymorphism enables objects to be treated as instances of their parent class, allowing them to be used interchangeably.

Function Overloading

Function overloading allows multiple functions with the same name but different parameters.

Operator Overloading

Operator overloading enables custom behavior for standard operators.

Virtual Functions

Virtual functions facilitate dynamic binding and runtime polymorphism.

Abstraction and Interfaces

Abstraction involves hiding implementation details to provide a simplified interface.

Abstract Classes

Abstract classes have at least one pure virtual function and cannot be instantiated.

Pure Virtual Functions

Pure virtual functions have no implementation and must be overridden by derived classes.

Interfaces in C++

Interfaces define a set of abstract methods that classes must implement.

Static Members

Static members are shared among all objects of a class.

Static Data Members

Static data members have a single instance shared across all objects.

Static Member Functions

Static member functions can be called without creating an object of the class.

C++ Standard Template Library (STL)

The STL is a collection of template classes and functions that offer data structures and algorithms for efficient programming.

Containers

Containers hold collections of objects, like vectors, lists, and maps.

Iterators

Iterators provide a way to traverse container elements.

Algorithms

Algorithms are generic functions that work on containers, performing operations like sorting and searching.

Real-time Examples of OOP in C++

1. Building a Banking System

Use OOP concepts to design a banking system with account classes, transaction history, and customer interactions.

2. Developing a Game Engine

Leverage OOP to create a game engine with classes for entities, rendering, and game mechanics.

3. Creating a Shapes Hierarchy

Design a shapes hierarchy with classes for geometric shapes, demonstrating inheritance and polymorphism.

Best Practices and Tips for OOP Interviews

1. Understand the Problem Statement

Fully comprehend the problem requirements before designing a solution.

2. Demonstrate Modularity and Reusability

Create modular code with reusable components to showcase your OOP skills.

3. Handle Exceptional Cases

Account for edge cases and handle exceptions gracefully.

4. Use Standard Library Features

Leverage the C++ Standard Library to demonstrate familiarity with efficient data structures and algorithms.

Common Interview Questions on C++ OOP

1. Difference between Encapsulation and Abstraction

2. Explain the key distinctions between encapsulation and abstraction.

3. Why is Polymorphism Important?

4. Discuss the significance of polymorphism in OOP.

5. Explain Virtual Functions and Pure Virtual Functions

6. Elaborate on virtual functions and their role in polymorphism.

7. How to Achieve Multiple Inheritance in C++?

8. Detail different approaches to implement multiple inheritance in C++.

Conclusion

Mastering Object-Oriented Programming concepts in C++ is indispensable for cracking interviews and becoming a proficient software developer. By understanding the pillars of OOP, creating classes and objects, handling inheritance and polymorphism, and leveraging the C++ Standard Template Library, you can confidently tackle any interview question and impress employers with your coding skills.

FAQs

Q: Is C++ the only language that supports OOP?

A: No, many other programming languages, such as Java and C#, also support OOP concepts

2. Are all class members accessible within the class itself?

A: No, private members are accessible only within the class, while public members can be accessed from anywhere.

3. Q: Can you explain the difference between function overloading and operator overloading?

A: Function overloading involves defining multiple functions with the same name but different parameters, while operator overloading allows you to redefine the behavior of operators for custom types.

4. Q: Are abstract classes the same as interfaces?

A: While both abstract classes and interfaces have abstract methods, abstract classes can also have concrete methods, and they cannot be instantiated. Interfaces, on the other hand, are purely abstract and serve as contracts for classes to implement specific functionality.

5. Q: What is the advantage of using the C++ Standard Template Library (STL)?

A: The STL provides pre-built, efficient data structures and algorithms, saving developers time and effort in implementing common functionalities.