C++ Interview Questions – OOPs
1. [Asked in Infosys] What is Object-Oriented Programming (OOP) in C++?
Answer:
OOP (Object-Oriented Programming) is a programming paradigm based on the concept of objects, which contain data (attributes) and functions (methods) that operate on the data.
Key Features of OOP in C++:
- Encapsulation – Wrapping data and methods together in a single unit (class).
- Abstraction – Hiding implementation details from the user.
- Inheritance – Acquiring properties of one class in another.
- Polymorphism – Using a single interface to represent different types.
Example of OOP in C++:
#include <iostream>
using namespace std;
class Car {
public:
string brand;
void show() {
cout << "Car brand: " << brand;
}
};
int main() {
Car c1;
c1.brand = "Toyota";
c1.show();
return 0;
}
Output:
Car brand: Toyota
2. [Asked in TCS] What is a class and an object in C++?
Answer:
- Class: A blueprint for creating objects. It defines attributes (data members) and methods (member functions).
- Object: An instance of a class that contains real data.
Example:
class Employee {
public:
string name;
int id;
void display() {
cout << "Name: " << name << ", ID: " << id;
}
};
int main() {
Employee e1;
e1.name = "John";
e1.id = 101;
e1.display();
return 0;
}
Output:
Name: John, ID: 101
3. [Asked in Cognizant] What is the difference between structure and class in C++?
Answer:
| Feature | Structure (struct) | Class (class) |
|---|---|---|
| Access Specifier | Members are public by default | Members are private by default |
| Encapsulation | Not supported | Fully supports encapsulation |
| Inheritance | Not supported | Supported |
| Use Case | Data storage | OOP concepts |
Example:
struct Student {
string name; // Public by default
};
class Teacher {
string subject; // Private by default
};
4. [Asked in Wipro] What is encapsulation in C++?
Answer:
Encapsulation is the process of hiding data and restricting direct access to it. This protects data from unintended modifications.
Example:
#include <iostream>
using namespace std;
class BankAccount {
private:
double balance;
public:
void setBalance(double b) {
if (b >= 0)
balance = b;
}
double getBalance() {
return balance;
}
};
int main() {
BankAccount acc;
acc.setBalance(1000);
cout << "Balance: " << acc.getBalance();
return 0;
}
Output:
Balance: 1000
Encapsulation ensures that data is accessed only through controlled methods.
5. [Asked in IBM] What is inheritance in C++? Explain types of inheritance.
Answer:
Inheritance allows a class (child) to acquire properties and methods from another class (parent).
Types of Inheritance in C++:
- Single Inheritance – One class inherits from another.
- Multiple Inheritance – A class inherits from multiple base classes.
- Multilevel Inheritance – A class inherits from another derived class.
- Hierarchical Inheritance – Multiple classes inherit from a single base class.
- Hybrid Inheritance – Combination of multiple inheritance types.
Example of Single Inheritance:
class Vehicle {
public:
void run() {
cout << "Vehicle is running";
}
};
class Car : public Vehicle {};
int main() {
Car c;
c.run(); // Inherited from Vehicle
return 0;
}
Output:
Vehicle is running
6. [Asked in Deloitte] What is polymorphism in C++? Explain types.
Answer:
Polymorphism allows one interface to have multiple implementations.
Types of Polymorphism:
- Compile-time Polymorphism (Function Overloading, Operator Overloading)
- Run-time Polymorphism (Method Overriding using Virtual Functions)
Example of Function Overloading:
class Math {
public:
int add(int a, int b) {
return a + b;
}
double add(double a, double b) {
return a + b;
}
};
int main() {
Math obj;
cout << obj.add(5, 10) << endl; // Calls int version
cout << obj.add(3.5, 2.5); // Calls double version
return 0;
}
Output:
15
6.0
7. [Asked in Amazon] What is abstraction in C++?
Answer:
Abstraction is hiding implementation details and exposing only necessary functionality.
Example Using Abstract Class:
class Shape {
public:
virtual void draw() = 0; // Pure virtual function
};
class Circle : public Shape {
public:
void draw() override {
cout << "Drawing a Circle";
}
};
int main() {
Circle c;
c.draw();
return 0;
}
Output:
Drawing a Circle
Abstraction allows designing flexible and reusable code.
8. [Asked in Microsoft] What is a virtual function in C++?
Answer:
A virtual function is a function that is overridden in derived classes to support dynamic binding.
Example:
class Base {
public:
virtual void show() { cout << "Base class"; }
};
class Derived : public Base {
public:
void show() override { cout << "Derived class"; }
};
int main() {
Base *ptr;
Derived d;
ptr = &d;
ptr->show(); // Calls Derived class function
return 0;
}
Output:
Derived class
Virtual functions enable runtime polymorphism.
9. [Asked in Google] What is a constructor and a destructor in C++?
Answer:
- Constructor – A special function that initializes an object.
- Destructor – A special function that destroys an object when it goes out of scope.
Example:
class Demo {
public:
Demo() { cout << "Constructor Called"; }
~Demo() { cout << "Destructor Called"; }
};
int main() {
Demo d;
return 0;
}
Output:
Constructor Called
Destructor Called
10. [Asked in Flipkart] What is an interface in C++?
Answer:
An interface in C++ is implemented using pure virtual functions in an abstract class.
Example:
class Interface {
public:
virtual void display() = 0; // Pure virtual function
};
class Implement : public Interface {
public:
void display() override { cout << "Interface Implemented"; }
};
int main() {
Implement obj;
obj.display();
return 0;
}
Output:
Interface Implemented
