C++ Interview Questions and Answers(2025)

Introduction

C++ is one of the most widely used programming languages around the globe.  C++ provides programmers with extensive control over system resources and memory. It is also an object-oriented programming language, which gives programs a clear structure and enables code to be reused, lowering development costs.

C++ was created as an extension to C language, and the two languages have almost similar syntax. The major difference between C and C++ is that C++ supports classes and objects, whereas C does not. 

C++ is widely used in game development and servers and here are some of the real-world applications of C++ are as follows;

• GUI based applications
• Banking applications
• Distributed systems
• Database software
• Operating systems

In this blog, we will discuss some most-asked C++ interview questions. This will help you brush up on your concepts of C++ and prepare for your interviews.

C++ Interview Questions For Freshers

Here, we are going to discuss the top C++ interview questions.

1. What are class and objects in C++?

Ans. A class is a blueprint that defines the structure and behavior of objects. An instance of a class is called an object. Since a class is a user-defined data type, an object can be referred to as a variable of that data type. 

While objects are instances of classes that hold particular data and can perform operations specified by the class, classes define the structure and behavior of objects. 

2. What is STL in C++?

Ans. The STL in C++ is a powerful set of C++ template classes that provide general-purpose programming data and functions like vectors, lists, queues, and stacks. The STL is highly parameterized in its constituent parts.

STL is made up of three well-structured components, i.e., Algorithms, Containers, and Iterators.

3. What are destructors in C++?

Ans. A destructor is a member function of the class invoked when an object of that class goes out of scope or when the delete expression is used on a pointer to the object of that class. A destructor has the same name as their class name, but it is preceded by a tilde (~). Destructors in C++ cannot return any value or accept any parameters.

class Coding {
public:
  // Constructor for class Ninja
  Ninja();
  // Destructor for class Ninja
  ~Ninja();
};

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4. What are the different data types present in C++?

Ans.  Different Data Types in C++

Data types in C++ define the type of data a variable can store. They are essential in programming as they determine memory usage and the operations that can be performed on data. C++ provides four main categories of data types to handle different kinds of data effectively.

1. Primitive Data Types

Primitive data types are built-in types that can store fundamental values directly. These include:

• Integer (int): Stores whole numbers, e.g., int x = 10;
   
• Floating-point (float, double): Stores decimal numbers, e.g., float pi = 3.14;
   
• Character (char): Stores single characters, e.g., char letter = 'A';
   
• Boolean (bool): Stores true or false values, e.g., bool isAvailable = true;

2. Derived Data Types

Derived data types are created using primitive data types and help in managing complex data structures. These include:

• Arrays: A collection of elements of the same data type, e.g., int numbers[5] = {1, 2, 3, 4, 5};
   
• Pointers: Stores memory addresses, e.g., int* ptr = &x;
   
• References: Acts as an alias for another variable, e.g., int &ref = x;
   
• Function Pointers: Stores addresses of functions for dynamic function calls.

3. User-defined Data Types

These are structured data types created by programmers to represent real-world entities. Examples include:

• Structures (struct): Groups multiple variables, e.g.,

struct Student {
    string name;
    int age;
};

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• Classes (class): Used in Object-Oriented Programming to define objects, e.g.,

class Car {
    public:
        string brand;
        int year;
};

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• Enumerations (enum): Defines a set of named integer constants, e.g., enum Color {Red, Green, Blue};

4. Abstract Data Types

Abstract data types provide a higher level of abstraction and include:

• Stacks, Queues, Linked Lists: Implemented using classes and structures.
   
• Templates: Allow generic programming to handle different data types.

Importance of Data Types in C++

• Memory Management: Helps optimize memory usage by allocating appropriate space.
   
• Data Integrity: Prevents errors by restricting variables to specific types.
   
• Performance Optimization: Ensures efficient execution of operations based on data type constraints.
   

Understanding and using the right data type is essential for writing efficient and error-free C++ programs.

5. What is the difference between C and C++?

Ans. C and C++ are both powerful programming languages, but they differ in various aspects, such as programming paradigms, memory management, and features. The table below highlights the key differences between them:

C is best suited for system-level programming, while C++ is widely used in application development due to its object-oriented features.

6. What is the difference between equal to (==) and assignment operator (=)?

Ans. 

The == operator is mainly used for comparison, while the = operator is used for assigning values.

7. Why do we use static member variables?

Ans. 

• Shared Across All Objects: A static member variable is shared by all instances of a class, allowing data to be transferred among them. This is useful for storing common information like counters or flags.
   
• Memory Efficiency: Static variables are allocated only once, regardless of the number of objects created, which helps save memory, especially when dealing with large variables.

8. What is the use of a namespace in C++?

Ans. Namespace in C++ is used to group codes logically and to avoid name collisions that can occur when our code contains multiple libraries. At namespace scope, all identifiers are accessible to one another without qualification.

9. What is operator overloading in C++?

Ans. Most of the C++ operators can be redefined or are overloaded using operator overloading. It means operators can be provided with different meanings for a data type as per the user's choice. This functionality is known as operator overloading. 

10. What is the difference between reference and pointer in C++?

Ans.

11. What is the difference between call by value and call by reference?

Ans. 

Call by value is preferred when the function should not modify the original variable, whereas call by reference is used when changes need to reflect outside the function.

12. What do you know about friend class and friend function?

Ans. Friend Class: A friend class can access private and protected members of another class. It is declared using the friend keyword inside the target class.

Friend Function: A friend function can access private and protected members of a class without being a member itself. It is declared using the friend keyword.

Example of a Friend Function Accessing Private Members of Multiple Classes

#include <iostream>
using namespace std;

class ClassB; // Forward declaration

class ClassA {
private:
    int numA;
public:
    ClassA(int a) : numA(a) {}
    friend void showData(ClassA, ClassB); // Friend function declaration
};

class ClassB {
private:
    int numB;
public:
    ClassB(int b) : numB(b) {}
    friend void showData(ClassA, ClassB); // Friend function declaration
};

// Friend function definition
void showData(ClassA objA, ClassB objB) {
    cout << "ClassA numA: " << objA.numA << endl;
    cout << "ClassB numB: " << objB.numB << endl;
}

int main() {
    ClassA a(10);
    ClassB b(20);
    showData(a, b); // Calling the friend function
    return 0;
}

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Explanation:

• Forward Declaration: ClassB is forward-declared to be used in ClassA.
   
• Friend Function Declaration: The function showData is declared as a friend in both ClassA and ClassB to access private members.
   
• Friend Function Definition: It accepts objects of both classes and prints their private data.
   
• Main Function: Objects of ClassA and ClassB are created, and showData is called to access their private members.

13. Define Virtual function in C++?

Ans. A virtual function in C++ is a member function of a base class that we want to redefine in derived classes to achieve polymorphism. We can declare a virtual function in the base class using the virtual keyword in front of the function.

14. What is the OOPS concept in C++, and why do we need it?

Ans. Object Oriented Programming (OOP) is a programming paradigm that includes many principles such as inheritance, encapsulation, polymorphism, and so on. In earlier programming languages, such as C, we used procedural-oriented programming. This approach was not effective because it had some limitations, such as code that could not be reused in the program. So OOPS provides us with functionalities like code usability and data hiding.

15. How does the class accomplish data hiding in c++?

Ans. In C++, the class can divide data members and functions using three access specifiers: private, protected, and public. Here, private and protected members are hidden from the outside world and thus enable data hiding so that only relevant information is exposed to the user.