Top 30 Most Common Oops Interview Questions C++ You Should Prepare For

Landing a C++ development role often involves demonstrating a strong understanding of Object-Oriented Programming (OOP) principles. C++ is a cornerstone of many high-performance systems, from operating systems and game engines to financial trading platforms and embedded systems. Its power comes largely from its robust support for OOP paradigms. As a result, interviewers frequently probe candidates' knowledge of these core concepts. Mastering the common oops interview questions c++ is crucial for standing out and proving your foundational skills. This article dives into 30 frequently asked questions covering the essential aspects of OOP in C++, providing clear, concise, and answer-ready explanations to help you prepare effectively.

What Are oops interview questions c++?

oops interview questions c++ are technical interview questions designed to assess a candidate's understanding of Object-Oriented Programming concepts specifically within the context of the C++ language. These questions cover fundamental pillars like encapsulation, inheritance, polymorphism, and abstraction, as well as related features that support OOP in C++, such as classes, objects, constructors, destructors, virtual functions, templates, namespaces, and memory management techniques like smart pointers. Interviewers use these questions to gauge a candidate's theoretical knowledge, practical application skills, and ability to write clean, maintainable, and efficient C++ code that adheres to good OOP practices. They aim to ensure candidates can leverage C++'s OOP features effectively to build scalable and robust software systems.

Why Do Interviewers Ask oops interview questions c++?

Interviewers ask oops interview questions c++ for several key reasons. Firstly, OOP is a dominant paradigm in modern software development, and C++ is a powerful language that heavily utilizes it. A solid grasp of OOP principles demonstrates a candidate's ability to design structured, modular, and reusable code, which is essential for complex projects. Secondly, C++ has specific ways of implementing OOP concepts (e.g., multiple inheritance, virtual functions, explicit memory management), and questions about these specifics reveal a candidate's experience and depth of knowledge in the language itself. Understanding C++'s approach to OOP helps interviewers determine if a candidate can write efficient, safe, and idiomatic C++ code. Finally, these questions often serve as a starting point for deeper discussions about design patterns, memory safety, and performance implications, allowing interviewers to evaluate problem-solving skills and critical thinking. Excelling in oops interview questions c++ shows you can build reliable, maintainable C++ applications.

Preview List

1. What is the Difference Between C and C++?

2. Explain Inheritance.

3. What are Static Members and Static Member Functions?

4. What is Operator Overloading?

5. What is a Namespace in C++?

6. What are Templates in C++?

7. What is the Standard Template Library (STL)?

8. What are Smart Pointers in C++?

9. What are Lambda Expressions in C++?

10. What is Polymorphism in C++?

11. What is Encapsulation in C++?

12. What is Abstraction in C++?

13. What are Constructors and Destructors?

14. What is the Difference Between Call by Value and Call by Reference?

15. What is a Pointer in C++?

16. What is the Scope Resolution Operator?

17. How Do You Handle Exceptions in C++?

18. What is the Difference Between == and .equals() in C++?

19. What is a Copy Constructor?

20. What is a Friend Function?

21. What are the Different Types of Inheritance?

22. What is an Abstract Class?

23. What is a Pure Virtual Function?

24. How Do You Implement a Singleton Class in C++?

25. What is a Struct in C++?

26. What is a Union in C++?

27. What is the Difference Between Struct and Class in C++?

28. What is an Inline Function?

29. What is the Output of the Following Code?

30. How Do You Prevent Copying of Objects in C++?

1. What is the Difference Between C and C++?

Why you might get asked this:

To assess foundational knowledge and understanding of C++'s origin and its core addition: OOP. It sets the stage for deeper questions on C++-specific features.

How to answer:

Highlight that C++ is a superset of C, adding OOP features like classes, objects, inheritance, polymorphism, encapsulation, and abstraction. Mention other C++ features like templates, exceptions, and namespaces.

Example answer:

C is a procedural programming language, while C++ is an extension of C that supports object-oriented programming. C++ adds classes, objects, inheritance, polymorphism, encapsulation, and abstraction, along with features like templates, namespaces, and exception handling, which are not present in C.

2. Explain Inheritance.

Why you might get asked this:

A fundamental OOP concept. Evaluates your understanding of code reusability and class relationships, core to many oops interview questions c++.

How to answer:

Define inheritance as a mechanism where a new class (derived/child) acquires properties and behavior from an existing class (base/parent). Emphasize code reuse and establishing "is-a" relationships.

Example answer:

Inheritance is an OOP mechanism allowing a derived class to inherit members (data and methods) from a base class. This promotes code reuse and establishes a hierarchical relationship, meaning the derived class "is a type of" the base class.

3. What are Static Members and Static Member Functions?

Why you might get asked this:

Tests understanding of members that belong to the class itself rather than instances. Key for utility functions or shared data.

How to answer:

Explain that static members belong to the class, shared by all objects. Static member functions can access only static members and are called using the class name, not an object instance.

Example answer:

Static members are shared across all instances of a class, belonging to the class type itself. Static member functions can only access static data members and other static functions; they are called using the class name (ClassName::staticFunction()) without needing an object.

4. What is Operator Overloading?

Why you might get asked this:

Assesses knowledge of how C++ allows redefining operator behavior for custom types, enhancing code readability. Relevant for complex data structures.

How to answer:

Describe operator overloading as giving new meaning to existing C++ operators when applied to user-defined data types. Explain it improves code expressiveness and readability for custom objects.

Example answer:

Operator overloading allows you to redefine how standard operators like +, -, ==, etc., behave when applied to instances of user-defined classes. This makes code using custom objects more intuitive and readable, like adding two complex numbers using the + operator.

5. What is a Namespace in C++?

Why you might get asked this:

Tests knowledge of scope management and preventing naming conflicts, essential for large C++ projects.

How to answer:

Explain namespaces as a mechanism to group related identifiers (classes, functions, variables) under a unique name. State their primary purpose is to prevent naming collisions, especially when combining code from different libraries.

Example answer:

A namespace is a declarative region that provides a scope to the identifiers inside it (types, functions, variables, etc.). Its main purpose is to prevent name conflicts by grouping related code, allowing different libraries to use the same identifier names without collision.

6. What are Templates in C++?

Why you might get asked this:

Evaluates understanding of generic programming and compile-time polymorphism, crucial for writing reusable, type-safe code like containers.

How to answer:

Define templates as a feature enabling functions and classes to operate with generic types. Explain they are used for creating reusable code structures (like algorithms or data structures) that work on any data type, providing compile-time polymorphism.

Example answer:

Templates allow you to write generic code that can work with any data type. Class templates are used for generic containers (like std::vector), and function templates for generic algorithms (like std::sort). They provide compile-time polymorphism, ensuring type safety.

7. What is the Standard Template Library (STL)?

Why you might get asked this:

Checks familiarity with the standard C++ library components, which are heavily used in modern C++ development and demonstrate practical knowledge.

How to answer:

Describe STL as a powerful collection of C++ template classes and functions providing common data structures (containers like vector, list, map) and algorithms (sort, find). Mention its components: containers, algorithms, iterators, and function objects.

Example answer:

The Standard Template Library (STL) is a part of the C++ standard library. It's a collection of generic classes and functions, primarily templates, providing fundamental data structures (like std::vector, std::map), algorithms (std::sort, std::find), and other components like iterators.

8. What are Smart Pointers in C++?

Why you might get asked this:

Tests understanding of modern C++ memory management practices, crucial for avoiding common pitfalls like memory leaks and dangling pointers.

How to answer:

Explain smart pointers (std::uniqueptr, std::sharedptr, std::weak_ptr) as RAII wrappers around raw pointers that automatically manage memory deallocation. Highlight how they prevent memory leaks and simplify resource management.

Example answer:

Smart pointers are objects that act like pointers but automatically manage the memory they point to, typically using RAII. They ensure that the memory is deallocated when the smart pointer goes out of scope, preventing memory leaks. Examples include uniqueptr (exclusive ownership) and sharedptr (shared ownership).

9. What are Lambda Expressions in C++?

Why you might get asked this:

Assesses knowledge of modern C++ features, specifically inline anonymous functions, useful for functional programming paradigms and algorithms.

How to answer:

Define lambda expressions as inline, anonymous functions that can capture variables from their surrounding scope. Explain they are often used for concise, one-off functions passed to algorithms or event handlers.

Example answer:

Lambda expressions are anonymous functions you can define and use inline. They are convenient for creating small function objects, often used with STL algorithms (std::for_each, std::sort) or when a short, specific function is needed without a formal definition. They can capture variables from the enclosing scope.

10. What is Polymorphism in C++?

Why you might get asked this:

A core OOP pillar. Evaluates understanding of how objects of different classes can respond to the same method call in different ways, critical for flexible designs.

How to answer:

Define polymorphism ("many forms") as the ability of objects of different types to respond to the same message (method call) in different ways. Explain the two main types in C++: compile-time (function/operator overloading) and runtime (virtual functions/pointers/references).

Example answer:

Polymorphism allows objects of different classes to be treated as objects of a common base class, and a method call behaves according to the actual object type at runtime. C++ supports compile-time polymorphism (overloading) and runtime polymorphism (virtual functions).

11. What is Encapsulation in C++?

Why you might get asked this:

Another core OOP pillar. Tests understanding of data hiding and bundling data with methods, essential for modularity and data integrity.

How to answer:

Describe encapsulation as the bundling of data (member variables) and the methods (member functions) that operate on that data into a single unit, the class. Explain its key aspect is data hiding, controlling access (public, protected, private) to protect data integrity.

Example answer:

Encapsulation is the practice of bundling data and the methods that operate on that data within a single unit, typically a class. It involves data hiding through access specifiers (private, protected), restricting direct external access to the data and controlling modifications only through defined methods.

12. What is Abstraction in C++?

Why you might get asked this:

Tests understanding of hiding complexity and focusing on essential features, another fundamental OOP pillar important for managing large systems.

How to answer:

Define abstraction as the concept of hiding complex implementation details while only exposing the necessary features or interfaces to the user. Use abstract classes and interfaces as C++ examples.

Example answer:

Abstraction focuses on representing essential features without including background details. In C++, this is achieved through abstract classes and interfaces (pure virtual functions), where the user interacts with a simplified view without needing to know the complex internal workings.

13. What are Constructors and Destructors?

Why you might get asked this:

Fundamental to object lifecycle management in C++. Tests understanding of how objects are initialized and cleaned up.

How to answer:

Explain constructors as special member functions that initialize an object when it's created. Explain destructors as special member functions called when an object goes out of scope or is explicitly deleted, used for cleanup and resource release.

Example answer:

Constructors are called automatically when an object is created, used to initialize its members. Destructors are called automatically when an object is destroyed (e.g., goes out of scope or delete is used), used to release resources like dynamically allocated memory.

14. What is the Difference Between Call by Value and Call by Reference?

Why you might get asked this:

Core concept in function parameter passing, impacting performance and how functions interact with variables.

How to answer:

Explain call by value passes a copy of the argument, so changes inside the function don't affect the original variable. Explain call by reference passes a reference (or pointer), allowing the function to modify the original variable.

Example answer:

In call by value, a function receives a copy of the argument; modifications inside the function don't affect the original variable. In call by reference (using references or pointers), a function gets access to the original variable's memory location, so changes inside the function directly modify the original variable.

15. What is a Pointer in C++?

Why you might get asked this:

Fundamental C++ concept, crucial for manual memory management and low-level operations, often linked to understanding underlying OOP implementation.

How to answer:

Define a pointer as a variable that stores the memory address of another variable. Explain its use in accessing and manipulating data indirectly via memory addresses, manual memory allocation (new, delete), and implementing data structures.

Example answer:

A pointer is a variable that stores the memory address of another variable. It allows indirect access to data stored elsewhere. Pointers are fundamental for dynamic memory allocation, working with arrays, and implementing data structures like linked lists.

16. What is the Scope Resolution Operator?

Why you might get asked this:

Tests understanding of accessing members in different scopes, particularly class members outside the class definition or globally scoped items.

How to answer:

Explain :: as the scope resolution operator. State its primary use is to define a member function outside its class, access a class's static members, or access global variables when a local variable has the same name.

Example answer:

The scope resolution operator :: is used to identify and specify the context (scope) to which an identifier belongs. It's commonly used to define a class's member functions outside the class definition or to access static members of a class.

17. How Do You Handle Exceptions in C++?

Why you might get asked this:

Evaluates knowledge of structured error handling, a standard practice for robust applications.

How to answer:

Describe exception handling using try, catch, and optionally throw. Explain that code that might throw an exception goes in the try block, and the code to handle specific exception types goes in corresponding catch blocks.

Example answer:

Exception handling in C++ is done using try, catch, and throw. Code that may generate an exception is placed in a try block. If an exception occurs, it is thrown and caught by a suitable catch block, which handles the error gracefully.

18. What is the Difference Between == and .equals() in C++?

Why you might get asked this:

A trickier question for those familiar with Java/C#. Tests specific C++ operator behavior and library conventions vs. built-in language features.

How to answer:

Explain that == is the equality operator, used for value comparison (or pointer comparison). State that .equals() is not a built-in or standard method in C++; equality comparison is typically done using the overloaded == operator.

Example answer:

In C++, == is the standard equality operator, used for comparing primitive types by value or comparing pointers by address. The .equals() method does not exist as a standard feature in C++ like it does in Java; custom equality comparison for objects is achieved by overloading the == operator.

19. What is a Copy Constructor?

Why you might get asked this:

Fundamental for object copying and passing objects by value. Tests understanding of how copies are made and the need for deep copying.

How to answer:

Define a copy constructor as a special constructor that creates a new object as a copy of an existing object of the same class. Explain it's called during initialization (e.g., passing by value, returning an object) and is crucial for handling resources (like dynamically allocated memory) to avoid shallow copies.

Example answer:

A copy constructor is a member function that initializes an object using another object of the same class. It's called when an object is passed by value, returned by value, or explicitly initialized from another object. It's vital for performing a deep copy of resources.

20. What is a Friend Function?

Why you might get asked this:

Tests understanding of controlled violation of encapsulation, useful in specific scenarios like operator overloading.

How to answer:

Define a friend function as a non-member function that is granted special permission by a class to access its private and protected members. Explain it's declared inside the class using the friend keyword but defined outside.

Example answer:

A friend function is a function declared with the friend keyword inside a class definition. It is not a member function but has permission to access the private and protected members of that class. This is often used for operator overloading or functions needing access to multiple classes' internals.

21. What are the Different Types of Inheritance?

Why you might get asked this:

Evaluates comprehensive knowledge of the inheritance mechanism, including variations and their complexities (like the diamond problem). Key for oops interview questions c++.

How to answer:

List and briefly describe the standard types: Single, Multiple, Multilevel, Hierarchical, and Hybrid. Focus on the structure of class relationships in each type.

Example answer:

C++ supports several types: Single (one base to one derived), Multiple (multiple bases to one derived), Multilevel (chain of inheritance), Hierarchical (one base to multiple derived), and Hybrid (combination of types, often multiple and multilevel).

22. What is an Abstract Class?

Why you might get asked this:

Tests understanding of designing base classes that cannot be instantiated but serve as interfaces or common bases for derived classes. Related to abstraction and polymorphism.

How to answer:

Define an abstract class as a class that cannot be instantiated directly. Explain it typically contains one or more pure virtual functions and serves as a base class to be inherited by concrete classes, enforcing an interface.

Example answer:

An abstract class is a class designed to be inherited from, not instantiated directly. It contains at least one pure virtual function. Abstract classes define a common interface or structure that derived classes must implement, serving as blueprints for related objects.

23. What is a Pure Virtual Function?

Why you might get asked this:

Specific C++ feature enabling abstract classes and enforcing interface implementation in derived classes. Crucial for runtime polymorphism.

How to answer:

Define a pure virtual function as a virtual function declared in a base class with = 0; syntax, having no implementation in the base class. State that any class inheriting from a base with a pure virtual function must provide an implementation or become abstract itself.

Example answer:

A pure virtual function is a virtual function in a base class that is declared using = 0; and has no implementation in the base class. It forces derived classes to provide their own implementation, making the base class abstract and defining an interface for its subclasses.

24. How Do You Implement a Singleton Class in C++?

Why you might get asked this:

Common design pattern question related to object creation control. Tests understanding of static members, constructors, and controlled access.

How to answer:

Describe the pattern: private constructor, private static instance variable, and a public static method to get the instance. Provide a basic code structure emphasizing controlled access and lazy initialization.

Example answer:

A singleton ensures only one instance exists. Implement with a private constructor, a private static pointer to the instance, and a public static method (getInstance) that creates the instance on first call and returns it.

class Singleton {
private:
    static Singleton* instance;
    Singleton() {} // Private constructor
public:
    static Singleton* getInstance() {
        if (instance == nullptr) {
            instance = new Singleton();
        }
        return instance;
    }
    // Disable copy/assignment
    Singleton(const Singleton&) = delete;
    Singleton& operator=(const Singleton&) = delete;
    // Add a destructor for cleanup if needed
};
Singleton* Singleton::instance = nullptr; // Initialize static member

25. What is a Struct in C++?

Why you might get asked this:

Tests understanding of aggregate data types and their subtle differences from classes in C++.

How to answer:

Define a struct as a user-defined data type that can contain members (data and functions). State its primary difference from a class in C++ is that its members have public access by default, whereas class members are private by default.

Example answer:

A struct in C++ is similar to a class; it can contain data members and member functions. The key difference is the default access specifier: members of a struct are public by default, while members of a class are private by default.

26. What is a Union in C++?

Why you might get asked this:

Tests understanding of memory layout and how different data types can share the same memory space, useful for low-level programming or memory optimization.

How to answer:

Define a union as a special data type that allows different data types to be stored in the same memory location. Explain that only one member of the union can hold a value at any given time, and the size of the union is determined by its largest member.

Example answer:

A union is a data type where all members share the same memory location. Only one member can be active at a time. Unions are useful for saving memory when you know you only need one of several possible values stored, but they require careful management.

27. What is the Difference Between Struct and Class in C++?

Why you might get asked this:

Reiterates understanding of struct vs class, focusing on the default access specifier which is the primary distinction in C++.

How to answer:

State clearly that the only practical difference in C++ is the default member access: struct members are public by default, and class members are private by default.

Example answer:

The main difference between a struct and a class in C++ is the default member access level. For a struct, members are public by default. For a class, members are private by default. Otherwise, their capabilities are identical.

28. What is an Inline Function?

Why you might get asked this:

Tests understanding of compiler optimizations and function call overhead reduction.

How to answer:

Define an inline function as a function whose code the compiler is requested to substitute directly at the call site instead of performing a traditional function call. Explain the goal is to reduce function call overhead, potentially improving performance, though the compiler makes the final decision.

Example answer:

An inline function is a hint to the compiler to replace the function call with the function's body code directly at the point of the call. This can reduce the overhead of function calls, particularly for small, frequently called functions, potentially improving performance.

29. What is the Output of the Following Code?

Why you might get asked this:

A common test of understanding operator precedence, side effects, and undefined behavior in C++.

How to answer:

Explain that applying the post-increment operator (++) multiple times to the same variable within a single expression results in undefined behavior according to the C++ standard, likely causing a compiler error or unpredictable results.

Example answer:

The expression (a++)++ attempts to modify a multiple times without an intervening sequence point. According to the C++ standard, this results in undefined behavior. Compilers will typically issue an error.

30. How Do You Prevent Copying of Objects in C++?

Why you might get asked this:

Tests understanding of copy control and resource management, essential for classes managing unique resources or requiring strict singleton behavior.

How to answer:

Explain that you prevent copying by explicitly deleting the copy constructor and the copy assignment operator (operator=). This tells the compiler not to generate default versions and makes any attempt to copy a compile-time error.

Example answer:

To prevent object copying, explicitly delete the copy constructor and copy assignment operator using = delete;. This disables the compiler-generated default versions and makes copying attempts a compile-time error.

class NonCopyable {
public:
    NonCopyable() = default;
    // Delete copy constructor and assignment operator
    NonCopyable(const NonCopyable&) = delete;
    NonCopyable& operator=(const NonCopyable&) = delete;
};

Other Tips to Prepare for a oops interview questions c++

Preparing thoroughly for oops interview questions c++ involves more than just memorizing definitions. Practice writing code that demonstrates these concepts. Implement simple examples of inheritance, polymorphism using virtual functions, encapsulation with access specifiers, and smart pointer usage. "The only way to learn a new programming language is by writing programs in it," says computing pioneer Dennis Ritchie. Work through coding problems that require applying OOP principles. Consider using a tool like Verve AI Interview Copilot (https://vervecopilot.com) to practice explaining these concepts aloud and get feedback on your clarity and confidence. Verve AI Interview Copilot can simulate interview scenarios, helping you refine your responses to common oops interview questions c++. Don't just explain polymorphism; be ready to write a small example demonstrating a virtual function. Similarly, be prepared to discuss real-world scenarios where you've applied encapsulation or used smart pointers to manage resources. As Bjarne Stroustrup, the creator of C++, puts it, "Design and programming are human activities; forget that and all is lost." Focus on understanding the why behind each OOP concept and C++ feature, not just the what. Practice explaining your code and design choices concisely. Use resources like cppreference.com or effective C++ books to deepen your understanding of C++ specifics. Verve AI Interview Copilot is designed to help you articulate these technical details effectively.

Frequently Asked Questions

Q1: What is the difference between a shallow and deep copy?
A1: Shallow copy copies member values; deep copy copies values and duplicates resources pointed to by pointers, preventing shared resource issues.

Q2: When would you use a virtual destructor?
A2: Use a virtual destructor in a base class when you have virtual functions to ensure correct destruction of derived objects via base pointers.

Q3: What is RAII?
A3: Resource Acquisition Is Initialization: Tie resource lifetime to object lifetime. Resource is acquired in constructor, released in destructor.

Q4: What is function overloading?
A4: Defining multiple functions with the same name but different parameter lists in the same scope.

Q5: What is method overriding?
A5: Providing a specific implementation of a virtual function in a derived class that is already defined in the base class.

Q6: Can a destructor be virtual?
A6: Yes, and it should be if the class is intended to be a base class with virtual functions, to ensure proper cleanup.