Top 30 Most Common c++ interview questions and answers You Should Prepare For
Landing a job in C++ development requires more than just technical skills; it demands confidence, clarity, and the ability to articulate your knowledge effectively. Preparing for c++ interview questions and answers is crucial. Mastering commonly asked c++ interview questions and answers can significantly boost your interview performance, giving you the edge you need to succeed. The ability to clearly and concisely explain complex C++ concepts is what sets apart good candidates from great ones. Verve AI’s Interview Copilot is your smartest prep partner—offering mock interviews tailored to C++ roles. Start for free at Verve AI.
What are c++ interview questions and answers?
C++ interview questions and answers are inquiries designed to assess a candidate's understanding of the C++ programming language, its core principles, and practical applications. These questions span various topics, including object-oriented programming (OOP), data structures, algorithms, memory management, and the Standard Template Library (STL). They are important because they help employers gauge a candidate's ability to write efficient, maintainable, and robust code. The scope of c++ interview questions and answers can range from basic syntax and concepts to advanced design patterns and system-level programming.
Why do interviewers ask c++ interview questions and answers?
Interviewers ask c++ interview questions and answers to evaluate several key aspects of a candidate's suitability for a role. They're not just looking for rote memorization of syntax. They aim to assess:
Technical Knowledge: Do you understand the fundamentals of C++ and its advanced features?
Problem-Solving Ability: Can you apply your knowledge to solve real-world programming challenges?
Practical Experience: Have you worked on projects that demonstrate your C++ skills?
Communication Skills: Can you clearly and concisely explain your thought process and solutions?
Ultimately, interviewers want to determine if you possess the skills and understanding necessary to contribute effectively to their team. Preparing for c++ interview questions and answers will ensure you demonstrate your capabilities effectively. You’ve seen the top questions—now it’s time to practice them live. Verve AI gives you instant coaching based on real company formats. Start free: https://vervecopilot.com.
Here's a preview of the 30 most common c++ interview questions and answers we'll be covering:
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:
int a = 1; int x = (a++)++;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:
This question is fundamental and assesses your understanding of the evolution of C++ from C. It tests your knowledge of the core differences in paradigms and features, and your ability to explain how C++ enhances C. Interviewers use this question about c++ interview questions and answers to gauge your foundational knowledge.
How to answer:
Highlight that C is a procedural language, while C++ is object-oriented. Emphasize the key features that C++ adds, such as classes, inheritance, and polymorphism. Briefly mention C++'s improved memory management and other advantages.
Example answer:
"Well, C is a procedural language focused on step-by-step execution, whereas C++ builds on that foundation by introducing object-oriented programming principles. In a recent project, I leveraged C++ classes and inheritance to create a more modular and reusable codebase, which would have been significantly harder to achieve in pure C. So, while C++ includes C, it provides tools for more complex and organized software design."
## 2. Explain Inheritance.
Why you might get asked this:
Inheritance is a cornerstone of object-oriented programming. Interviewers want to see if you understand how it promotes code reuse and modularity. This is a common question amongst many c++ interview questions and answers.
How to answer:
Define inheritance as a mechanism where a child class inherits properties and methods from a parent class. Explain its benefits, such as code reuse and creating hierarchical relationships between classes.
Example answer:
"Inheritance is a way to create new classes based on existing ones. For example, in a game development project, I had a base 'GameObject' class with properties like position and visibility. Then, I created derived classes like 'Enemy' and 'Player' that inherited those basic properties but added their own unique behaviors. This not only saved me time but also ensured a consistent structure across all game objects, which is why it’s such a vital part of the c++ interview questions and answers."
## 3. What are static members and static member functions?
Why you might get asked this:
This question probes your understanding of how static members are shared across all instances of a class. It tests your knowledge of memory management and scoping.
How to answer:
Explain that static members belong to the class itself, not to individual objects. Describe how static member functions can only access static members and don't have a this pointer.
Example answer:
"Static members are essentially variables that are shared among all instances of a class. In a logging system I built, I used a static counter to track the total number of log entries created. Static member functions can then access and manipulate those static members without needing an object instance. It’s a useful way to manage shared state, that I’ve learned is a key aspect of c++ interview questions and answers."
## 4. What is operator overloading?
Why you might get asked this:
Operator overloading demonstrates your ability to make code more intuitive and readable by defining custom behavior for operators.
How to answer:
Explain that operator overloading allows you to redefine the behavior of operators for user-defined types. Give an example of how this can make code more expressive.
Example answer:
"Operator overloading lets you define how standard operators like +, -, *, etc., behave with your own custom classes. In a matrix library I developed, I overloaded the + operator to perform matrix addition. This allowed users to add matrices using a natural syntax (matrix1 + matrix2) instead of calling a separate function, which is often an important part of c++ interview questions and answers. This greatly improved the readability and usability of the library."
## 5. What is a namespace in C++?
Why you might get asked this:
Namespaces are essential for avoiding naming conflicts, especially in large projects. This question tests your understanding of code organization and modularity.
How to answer:
Define a namespace as a way to group related classes, functions, and variables under a common name, preventing naming collisions.
Example answer:
"A namespace is a way to create a scope for identifiers, like class names and function names, to prevent conflicts when using code from different libraries or modules. For example, in a project involving multiple sensor types, I put each sensor's code into its own namespace to avoid naming collisions between functions like 'readData'. I always think about this in relation to c++ interview questions and answers."
## 6. What are templates in C++?
Why you might get asked this:
Templates are a powerful feature for writing generic code. This question assesses your ability to write code that works with different data types without sacrificing type safety.
How to answer:
Explain that templates allow you to write functions and classes that operate on generic types. Highlight the benefits of code reusability and type safety.
Example answer:
"Templates allow you to write code that can work with different data types without having to write separate versions for each type. I used templates extensively when creating a generic sorting algorithm that could sort arrays of integers, floats, or custom objects. It’s something interviewers ask as it relates to c++ interview questions and answers and generic programming."
## 7. What is the Standard Template Library (STL)?
Why you might get asked this:
The STL is a fundamental part of C++. Knowing its components and how to use them is crucial for efficient development.
How to answer:
Describe the STL as a collection of C++ libraries that provide common data structures and algorithms. Mention examples like vectors, lists, and maps.
Example answer:
"The STL is a collection of pre-built data structures and algorithms that come with C++. It includes things like vectors, lists, maps, and algorithms for sorting, searching, and transforming data. When solving a data processing task, I heavily rely on STL containers and algorithms to avoid reinventing the wheel, which is why its important in c++ interview questions and answers."
## 8. What are smart pointers in C++?
Why you might get asked this:
Smart pointers are essential for memory management and preventing memory leaks. This question assesses your understanding of resource management in C++.
How to answer:
Explain that smart pointers are classes that automatically manage the lifetime of dynamically allocated objects, preventing memory leaks. Mention the different types of smart pointers: uniqueptr, sharedptr, and weak_ptr.
Example answer:
"Smart pointers are a way to automatically manage memory in C++. They are designed to prevent memory leaks by automatically deleting dynamically allocated objects when they are no longer needed. I always use smart pointers like uniqueptr for exclusive ownership and sharedptr for shared ownership to ensure proper memory management in my projects. Smart pointers are a hot topic in many c++ interview questions and answers."
## 9. What are lambda expressions in C++?
Why you might get asked this:
Lambda expressions allow you to create small, anonymous functions inline. This question tests your knowledge of modern C++ features and functional programming concepts.
How to answer:
Describe lambda expressions as small, anonymous functions that can be defined inline within a larger expression. Explain their use cases, such as creating short functions for algorithms.
Example answer:
"Lambda expressions are essentially short, unnamed functions that you can define directly in your code, often used as arguments to other functions. In a data processing pipeline, I used a lambda expression to filter a vector of data points based on a specific condition. Lambdas are very useful to show you’re up-to-date on c++ interview questions and answers"
## 10. What is polymorphism in C++?
Why you might get asked this:
Polymorphism is a fundamental OOP concept. This question assesses your understanding of how objects can take on multiple forms.
How to answer:
Explain that polymorphism is the ability of an object to take on many forms. Describe how it's achieved through method overriding and method overloading.
Example answer:
"Polymorphism is the ability of an object to take on multiple forms. I've used it, for example, in a drawing program where I have a base class 'Shape' and derived classes like 'Circle' and 'Rectangle'. Each derived class implements its own 'draw' method. When I call the 'draw' method on a collection of 'Shape' objects, the correct 'draw' method for each specific shape is called."
## 11. What is encapsulation in C++?
Why you might get asked this:
Encapsulation is key to data integrity and abstraction. This question tests your understanding of how to protect data within a class.
How to answer:
Explain that encapsulation is the concept of bundling data and methods that operate on that data within a class, and hiding internal data from the outside world.
Example answer:
"Encapsulation is all about bundling data and the methods that operate on that data within a class, while hiding the internal details from the outside world. In a banking application, I encapsulated the account balance within an 'Account' class and provided methods like 'deposit' and 'withdraw' to access and modify it. This prevented direct access to the balance, ensuring data integrity."
## 12. What is abstraction in C++?
Why you might get asked this:
Abstraction simplifies complex systems. This question assesses your ability to hide implementation details and expose only essential information.
How to answer:
Explain that abstraction involves exposing only the necessary information while hiding the background details.
Example answer:
"Abstraction is about simplifying complex systems by only showing the essential details to the user while hiding the underlying implementation complexity. In a car simulation, the user interacts with the car through simple controls like steering and acceleration, without needing to know the intricate details of the engine or braking system."
## 13. What are constructors and destructors?
Why you might get asked this:
Constructors and destructors are fundamental for object lifecycle management. This question tests your understanding of how objects are initialized and cleaned up.
How to answer:
Explain that constructors are called when an object is created, and destructors are called when an object is destroyed.
Example answer:
"Constructors are special member functions that are automatically called when you create an object of a class, and destructors are called when the object is destroyed. In a file management system, I used a constructor to open a file when an object was created and a destructor to automatically close the file when the object was no longer needed. These basics can be important parts of c++ interview questions and answers"
## 14. What is the difference between call by value and call by reference?
Why you might get asked this:
Understanding how arguments are passed to functions is crucial for avoiding unintended side effects and optimizing performance.
How to answer:
Explain that call by value passes a copy of the original value, while call by reference passes a reference to the original variable.
Example answer:
"Call by value passes a copy of the variable's value to the function, so any changes made inside the function don't affect the original variable. Call by reference, on the other hand, passes a reference to the original variable, so changes made inside the function do affect the original variable. If you mention it during your c++ interview questions and answers, you’ll definitely impress the interviewer."
## 15. What is a pointer in C++?
Why you might get asked this:
Pointers are a core concept in C++. This question assesses your understanding of memory addresses and how to manipulate them.
How to answer:
Define a pointer as a variable that holds the memory address of another variable.
Example answer:
"A pointer is a variable that stores the memory address of another variable. In a system programming task, I used pointers to directly access and manipulate memory locations to optimize performance."
## 16. What is the scope resolution operator?
Why you might get asked this:
This operator is essential for resolving naming conflicts and accessing members of classes and namespaces.
How to answer:
Explain that the scope resolution operator (::) is used to access members of classes, namespaces, and global variables when there are naming conflicts.
Example answer:
"The scope resolution operator (::) is used to access members of a class or namespace when there's ambiguity. For example, if a global variable has the same name as a local variable, I can use the scope resolution operator to specifically access the global variable from within a function."
## 17. How do you handle exceptions in C++?
Why you might get asked this:
Exception handling is crucial for writing robust and fault-tolerant code. This question assesses your ability to handle errors gracefully.
How to answer:
Explain that exceptions are handled using try-catch blocks. The try block contains the code that might throw an exception, and the catch block handles it.
Example answer:
"Exceptions are handled using try-catch blocks. I wrap the code that might throw an exception in a try block, and then I use one or more catch blocks to handle specific types of exceptions. This prevents the program from crashing and allows me to handle errors gracefully."
## 18. What is the difference between == and .equals() in C++?
Why you might get asked this:
This question is a bit of a trick, designed to see if you're familiar with the nuances of C++ versus other languages like Java.
How to answer:
Explain that in C++, == is the equality operator for comparing values and there is no .equals() method like in Java.
Example answer:
"In C++, == is the equality operator used for comparing values. C++ doesn't have an .equals() method like Java. So, when comparing objects, the behavior of == depends on whether it's been overloaded for that specific class."
## 19. What is a copy constructor?
Why you might get asked this:
Copy constructors are essential for creating copies of objects correctly. This question assesses your understanding of object lifecycle and memory management.
How to answer:
Explain that a copy constructor is a special constructor that creates a copy of an existing object.
Example answer:
"A copy constructor is a special constructor that's called when you create a new object as a copy of an existing object. If I don't define a copy constructor for a class that contains pointers, the default copy constructor will simply copy the pointer values, leading to both objects pointing to the same memory location. So, it should be addressed in c++ interview questions and answers."
## 20. What is a friend function?
Why you might get asked this:
Friend functions can access private and protected members of a class. This question tests your understanding of access control and encapsulation.
How to answer:
Explain that a friend function is a function that can access the private and protected members of a class.
Example answer:
"A friend function is a function that's not a member of a class but can access its private and protected members. I used friend functions when designing operations between two classes, and the operation needs to directly access the internal data of both."
## 21. What are the different types of inheritance?
Why you might get asked this:
Understanding the different types of inheritance is essential for designing object-oriented systems effectively.
How to answer:
Mention single inheritance, multiple inheritance, multilevel inheritance, hierarchical inheritance, and hybrid inheritance.
Example answer:
"The different types are single inheritance (where a class inherits from one base class), multiple inheritance (where a class inherits from multiple base classes), multilevel inheritance (where a class inherits from a derived class, which in turn inherits from a base class), hierarchical inheritance (where multiple classes inherit from a single base class), and hybrid inheritance (a combination of multiple inheritance types)."
## 22. What is an abstract class?
Why you might get asked this:
Abstract classes are fundamental for defining interfaces and base classes in object-oriented programming.
How to answer:
Explain that an abstract class cannot be instantiated and is used to define an interface for other classes.
Example answer:
"An abstract class is a class that cannot be instantiated directly. It's used as a base class to define a common interface for its derived classes. It typically contains one or more pure virtual functions, making the derived classes define that function, so it’s a must-know topic for c++ interview questions and answers. "
## 23. What is a pure virtual function?
Why you might get asked this:
Pure virtual functions are key to defining abstract classes and enforcing implementation in derived classes.
How to answer:
Explain that a pure virtual function is a function declared in a base class that must be implemented by any non-abstract derived class.
Example answer:
"A pure virtual function is a virtual function that's declared in a base class but has no implementation. It's denoted by = 0 at the end of the function declaration. Any non-abstract derived class must provide an implementation for all pure virtual functions."
## 24. How do you implement a singleton class in C++?
Why you might get asked this:
Singleton classes are a common design pattern. This question assesses your ability to control object instantiation and ensure only one instance exists.
How to answer:
Explain that a singleton class is implemented by making the constructor private and providing a static method to get the instance.
Example answer:
"A singleton class ensures that only one instance of that class can be created. To implement it, you make the constructor private and provide a static method that returns the single instance of the class. The first time the static method is called, it creates the instance; subsequent calls simply return the existing instance."
## 25. What is a struct in C++?
Why you might get asked this:
Structs are similar to classes but have different default access specifiers. This question tests your understanding of data structures and access control.
How to answer:
Explain that a struct in C++ is similar to a class but defaults to public access for its members.
Example answer:
"A struct in C++ is similar to a class, but the main difference is that the members of a struct are public by default, while the members of a class are private by default. I think it's important to know this difference for c++ interview questions and answers."
## 26. What is a union in C++?
Why you might get asked this:
Unions allow you to store different data types in the same memory location. This question assesses your understanding of memory management and data representation.
How to answer:
Explain that a union is a special class type that can hold only one value at a time. All members share the same memory space.
Example answer:
"A union is a special type of class that can hold only one member at a time. All members of a union share the same memory location, so assigning a value to one member overwrites the values of all other members. This can be useful for saving memory when you know that only one of several possible data types will be used at any given time."
## 27. What is the difference between struct and class in C++?
Why you might get asked this:
This question clarifies your understanding of fundamental C++ concepts and default behaviors.
How to answer:
The primary difference is the default access specifier: public for structs and private for classes.
Example answer:
"The key difference is that, by default, members of a struct are public, while members of a class are private. Otherwise, they're largely the same - both can have methods, inheritance, etc. It’s another basic, but important thing to know for c++ interview questions and answers."
## 28. What is an inline function?
Why you might get asked this:
Inline functions can improve performance by reducing function call overhead. This question assesses your understanding of optimization techniques.
How to answer:
Explain that an inline function is expanded in-line by the compiler, potentially improving performance by reducing function call overhead.
Example answer:
"An inline function is a function that the compiler tries to expand in place, instead of performing a function call. This can improve performance by avoiding the overhead of a function call. I used them for short, frequently-called functions where the overhead of the function call was significant."
## 29. What is the output of the following code: int a = 1; int x = (a++)++;
Why you might get asked this:
This tests your understanding of postfix increment operators and sequence points in C++.
How to answer:
The output will be undefined because the increment operator is applied twice without a sequence point.
Example answer:
"The behavior of this code is undefined. You're trying to apply the postfix increment operator twice in a row without an intervening sequence point. The C++ standard doesn't specify the order in which these operations should be performed, so different compilers might produce different results, or the program might crash."
## 30. How do you prevent copying of objects in C++?
Why you might get asked this:
This assesses your understanding of object lifecycle management and preventing unintended copies.
How to answer:
You can prevent copying by deleting the copy constructor and copy assignment operator.
Example answer:
"You can prevent copying of objects by declaring the copy constructor and copy assignment operator as deleted. This tells the compiler not to generate these functions automatically, and any attempt to copy an object will result in a compilation error."
Other tips to prepare for a c++ interview questions and answers
Practice Coding: Solve coding challenges on platforms like LeetCode and HackerRank.
Review Data Structures and Algorithms: Master common data structures and algorithms.
Mock Interviews: Practice with friends or mentors to simulate the interview experience.
Understand Design Patterns: Familiarize yourself with common design patterns like Singleton, Factory, and Observer.
Stay Updated: Keep abreast of the latest C++ standards and features.
Reflect on Your Projects: Be prepared to discuss your past projects in detail.
Use AI tools: Leverage AI tools to improve your resume and interview preparation.
Preparing for c++ interview questions and answers requires dedication and practice. By mastering the concepts and questions outlined above, you'll be well-equipped to impress your interviewer and land your dream job.
"The only way to do great work is to love what you do." - Steve Jobs
Remember, success is not final, failure is not fatal: It is the courage to continue that counts.” – Winston Churchill
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Frequently Asked Questions
Q: What are the most important topics to study for a C++ interview?
A: Object-oriented programming principles, data structures and algorithms, memory management, and the Standard Template Library (STL) are crucial areas to focus on. Understanding exception handling and design patterns is also very important.
Q: How can I practice answering C++ interview questions?
A: Use online resources like LeetCode, HackerRank, and InterviewBit to practice coding problems. Participate in mock interviews with friends or mentors to simulate the interview experience.
Q: What should I do if I don't know the answer to a C++ interview question?
A: Be honest and admit that you don't know the answer. Then, try to explain your thought process and what approaches you would take to solve the problem. Showing your problem-solving skills can be just as important as knowing the correct answer.
Q: How important is it to have practical experience with C++?
A: Practical experience is highly valued. Be prepared to discuss your past projects in detail, including the challenges you faced and how you solved them. Use examples from your projects to illustrate your understanding of C++ concepts.
Q: What are some common mistakes to avoid during a C++ interview?
A: Avoid being arrogant or dismissive, and don't interrupt the interviewer. Be clear and concise in your answers, and avoid rambling. Most importantly, be honest and admit when you don't know something.
