Understanding Object-Oriented Programming (OOP) in C++

In this article I am going to explore and answer often asked programming interviews questions about oops, those are object-oriented programming in C++, OOP principles in C++, classes and objects in C++, inheritance in C++, polymorphism in C++, encapsulation in C++, let’s understand these concept with example.

In beginner-level interviews, candidates are often asked to explain or implement Object-Oriented Programming (OOP) concepts in C++. Interviewers might ask about classes, inheritance, polymorphism, encapsulation, and abstraction. Regardless of the exact wording, the expected response remains consistent.

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Understand OOP Concepts

As the title suggests, the interviewer will ask you to explain or implement OOP concepts using C++. Let’s break down these concepts through examples.

Classes and Objects

Class in C++:

Think of a class as a blueprint for creating objects, much like an architect’s plan for building houses. In the context of object-oriented programming in C++, a class defines the properties (attributes) and behaviours (methods) that the objects created from this blueprint will have.

For instance, if you were to create a class for a ‘Car’, it might include properties like colour, model, and engine size, as well as methods like start(), stop(), and accelerate(). This encapsulation in C++ allows for grouping related variables and functions together, promoting organised and manageable code.

Object in C++:

An object, on the other hand, is an instance of a class. Think of it as the actual house built from the architect’s blueprint. When you create an object, you’re essentially creating a specific ‘thing’ based on the class definition.

For example, using our ‘Car’ class, you might create an object called myCar which has a red colour, is a model from 2021, and has a 2.0-litre engine. This instantiation of the class means myCar can now use the start(), stop(), and accelerate() methods defined in the Car class. In terms of OOP principles in C++, objects are the concrete entities that embody the attributes and behaviours defined by their class.

#include <iostream>
#include <string>

using namespace std;

//----------------------- Class Part ----------------------
class Car {
public:
    string colour;
    string model;
    double engineSize;

    void start() {
        cout << "The " << model << " with a " << engineSize << " litre engine is starting." << endl;
    }

    void stop() {
        cout << "The " << model << " is stopping." << endl;
    }

    void accelerate() {
        cout << "The " << model << " is accelerating." << endl;
    }
};

//--------------------- Object Part ------------------------
int main() {
    Car myCar;
    myCar.colour = "Red";
    myCar.model = "Toyota Corolla";
    myCar.engineSize = 2.0;

    myCar.start();
    myCar.accelerate();
    myCar.stop();

    return 0;
}

Inheritance in C++:

Inheritance in C++ is like inheriting traits from your parents. It allows a class (called a derived class) to inherit properties and behaviours from another class (called a base class). This means the derived class can use the attributes and methods of the base class, while also having additional features or modified behaviours.

Inheritance is a core principle of object-oriented programming in C++, promoting code reusability and the creation of hierarchical relationships between classes.

Imagine you have a base class called ‘Animal’. This class includes common properties and methods that all animals share, such as age, weight, and methods like eat() and sleep(). Now, you create a derived class called ‘Bird’ that inherits from ‘Animal’. The ‘Bird’ class will have all the properties and methods of the ‘Animal’ class, but you can also add bird-specific features like wingSpan and methods like fly().

class Animal {
public:
    int age;
    double weight;

    void eat() {
        // implementation of eat
    }

    void sleep() {
        // implementation of sleep
    }
};

class Bird : public Animal {
public:
    double wingSpan;

    void fly() {
        // implementation of fly
    }
};

Polymorphism in C++

Polymorphism in C++ is akin to a Swiss Army knife, which can perform various tasks despite being a single tool. In the realm of object-oriented programming in C++, polymorphism allows objects of different classes to be treated as objects of a common base class. This means you can call the same method on different objects, and each object will respond in a manner appropriate to its class.

There are two main types of polymorphism in C++: compile-time (or static) polymorphism and runtime (or dynamic) polymorphism. Compile-time polymorphism is achieved through function overloading and operator overloading, while runtime polymorphism is achieved through inheritance and virtual functions.

Do not worry, I have separate in depth article for Polymorphism types in C++. please follow that page. beside that check below example of polymorphism.

class Animal {
public:
    virtual void speak() {
        cout << "Animal speaking" << endl;
    }
};

class Dog : public Animal {
public:
    void speak() override {
        cout << "Dog barking" << endl;
    }
};

int main() {
    Animal *animal = new Dog();
    animal->speak();  // Outputs: Dog barking

    delete animal;
    return 0;
}

Hard to understand above example ? let understand polymorphism with real world example.

So, think of polymorphism in C++ like having a universal remote control that works with any brand of TV. The remote (the base class) has a button labeled “power” (the draw() method). When you press this button, it sends the same signal regardless of the TV brand (Circle or Square). However, each TV interprets this signal in its own way and turns on accordingly. This flexibility is the essence of polymorphism, enabling one interface to control multiple forms of behaviour.

I trust that you’ve grasped how polymorphism works in object-oriented programming in C++. It’s a powerful feature that enhances flexibility and reuse in your code. Do not be afraid of the question if it arises again; just remember the analogy of the universal remote control, and you’ll have a clear understanding of polymorphism in C++.

Encapsulation and Abstraction in C++

Think of encapsulation in C++ like securing your precious jewellery in a safe. The safe (class) provides controlled access to your valuables (data) through a combination lock (methods). You decide who gets the combination and when, protecting your jewellery from unwanted access.

On the other hand, abstraction in C++ is like using an ATM machine. You interact with a simple interface—insert your card, enter your PIN, and select your transaction—without needing to know the intricate details of how the machine processes your request or manages the cash inside. The ATM presents a simplified interface, focusing on what it does, not how it does it.

if you are unable to understand do not worry at all, I have in depth article for both Encapsulation and Abstraction oops concepts. please follow that. beside that check below example.

#include <iostream>
using namespace std;

class BankAccount {
private:
    double balance;

public:
    BankAccount(double initialBalance) : balance(initialBalance) {}

    void deposit(double amount) {
        balance += amount;
    }

    void withdraw(double amount) {
        if (amount <= balance) {
            balance -= amount;
        } else {
            cout << "Insufficient funds" << endl;
        }
    }

    double getBalance() const {
        return balance;
    }

    void displayBalance() const {
        cout << "Current balance: $" << balance << endl;
    }
};

int main() {
    BankAccount myAccount(100.0);
    myAccount.displayBalance();

    myAccount.deposit(50.0);
    myAccount.displayBalance();

    myAccount.withdraw(30.0);
    myAccount.displayBalance();

    myAccount.withdraw(150.0); // Should display "Insufficient funds"
    myAccount.displayBalance();

    return 0;
}

I trust that you’ve grasped how encapsulation and abstraction work in object-oriented programming in C++. These principles are foundational to creating secure, modular, and easily understandable code. Do not be afraid of the question if it arises again; just remember the analogies of the safe and the ATM machine, and you’ll have a clear understanding of encapsulation and abstraction in C++.

Summarizing OOP Concepts in C++

In summary, understanding and implementing OOP concepts in C++ involves working with classes and objects, inheritance, polymorphism, encapsulation, and abstraction. These principles help structure programs in a clear, modular, and reusable way, which is essential for software development and interview preparation.

By following these steps, you can effectively explain and demonstrate OOP concepts in C++. If you have any questions or need further clarification, don’t hesitate to ask on our Quora space or use the form on our website. Good luck with your interviews!

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