Top 25 C++ Interview Questions with Detailed Answers (2026 Guide)

C++ is one of the most powerful and widely used programming languages in system programming, game development, embedded systems, and performance-critical applications. Because C++ gives developers low-level memory control along with high-level abstraction, interviewers frequently test deep conceptual understanding rather than just syntax knowledge.

This guide provides detailed explanations, examples, and interview insights to help both freshers and experienced developers crack technical interviews confidently.

1. What is C++?

C++ is a general-purpose programming language developed by Bjarne Stroustrup as an extension of the C language. It supports multiple programming paradigms including procedural programming, object-oriented programming (OOP), and generic programming.

C++ is widely used in operating systems, game engines, browsers, database systems, embedded devices, and high-frequency trading platforms because of its speed and memory control.

2. What are the main features of C++?

• Object-Oriented Programming – Supports classes and objects.
• Encapsulation – Data hiding using access specifiers.
• Inheritance – Code reusability.
• Polymorphism – Same interface, different behavior.
• Low-Level Memory Access – Pointers and manual memory control.
• Templates – Generic programming.
• STL – Built-in powerful data structures and algorithms.

3. Difference Between C and C++

C is a procedural programming language, whereas C++ supports object-oriented programming in addition to procedural programming.

4. What is OOP in C++?

Object-Oriented Programming (OOP) is a paradigm based on objects that contain data and methods. It improves modularity, reusability, and maintainability.

The four pillars of OOP:

• Encapsulation – Binding data and functions together.
• Abstraction – Hiding internal details.
• Inheritance – Reusing existing code.
• Polymorphism – Same function behaves differently.

Interview Tip: Be ready to explain these with real-world examples like “Car”, “Bank Account”, etc. 

5. What is a Class?

A class is a user-defined data type that acts as a blueprint for creating objects. It contains data members (variables) and member functions (methods).

class Car {
private:
    string brand;

public:
    void setBrand(string b) {
        brand = b;
    }

    void start() {
        cout << brand << " Car Started";
    }
};

6. What is an Object?

An object is an instance of a class. It occupies memory and can access class members.

Car c1;
c1.setBrand("BMW");
c1.start();

7. What is a Constructor?

A constructor is a special member function that is automatically called when an object is created. It initializes data members.

class Demo {
public:
    Demo() {
        cout << "Constructor Called";
    }
};

Types:

• Default Constructor
• Parameterized Constructor
• Copy Constructor

8. What is a Destructor?

A destructor is used to free resources when an object goes out of scope. It prevents memory leaks.

~Demo() {
   cout << "Destructor Called";
}

9. What is Function Overloading?

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

int add(int a, int b);
double add(double a, double b);

This improves code readability and flexibility. 

10. What is Operator Overloading?

Operator overloading allows redefining operators for user-defined types.

Example:

Complex operator + (Complex obj);

It allows objects to behave like primitive data types. 

11. What is a Pointer?

A pointer stores the memory address of another variable.

int a = 10;
int *ptr = &a;

Pointers are important for:

• Dynamic memory allocation
• Passing large objects efficiently
• Data structures (linked list, tree)

12. What is Dynamic Memory Allocation?

Dynamic memory is allocated during runtime using new and deallocated using delete.

int* ptr = new int(5);
delete ptr;

Failure to delete memory causes memory leaks.

13. What is Virtual Function?

A virtual function ensures runtime polymorphism using dynamic binding.

class Base {
public:
    virtual void show() {
        cout << "Base";
    }
};

If overridden in derived class, correct function is decided at runtime. 

14. What is Inheritance?

Inheritance allows a class (child) to inherit properties and behavior from another class (parent).

Types:

• Single
• Multiple
• Multilevel
• Hierarchical

15. What is Polymorphism?

Polymorphism means “many forms”. It can be:

• Compile-time (Function Overloading)
• Runtime (Virtual Functions)

16. What is Encapsulation?

Encapsulation hides internal data using private access specifiers and exposes only necessary functionality.

It improves security and maintainability. 

17. What is Abstraction?

Abstraction hides complex implementation details and shows only relevant functionality.

Example: You drive a car without knowing engine internals. 

18. What is STL?

STL (Standard Template Library) provides ready-made data structures and algorithms:

• vector
• map
• set
• stack
• queue

It improves performance and reduces development time. 

19. What is Template?

Templates enable generic programming.

template 
T add(T a, T b) {
    return a + b;
}

20. What is Namespace?

Namespace avoids naming conflicts in large projects.

namespace MyApp {
   int value = 10;
}

21. What is Inline Function?

An inline function suggests the compiler replace the function call with actual code to reduce overhead.

22. What is Exception Handling in C++?

try {
   throw 10;
}
catch(int e) {
   cout << "Exception Caught";
}

It prevents program crashes. ---

23. Difference Between Struct and Class

Default access specifier:

• struct → public
• class → private

Otherwise, both are almost identical in C++. 

24. What is const Keyword?

The const keyword makes variables immutable. It ensures data safety and prevents accidental modification.

25. What is the Difference Between Stack and Heap Memory?

• Stack – Stores local variables, fast, automatic memory management.
• Heap – Dynamic memory, manual allocation using new/delete.

Interviewers frequently ask this to test memory understanding.