Top 50 CPP Interview Questions

Basics and Fundamentals:

1. What is C++?

   • C++ is a general-purpose programming language developed as an extension of the C programming language. It supports both procedural and object-oriented programming paradigms.

2. Differentiate between C and C++.

   • C++ is an extension of C and includes features like classes, objects, and polymorphism, which are not present in C. C is procedural, while C++ supports both procedural and object-oriented programming.

3. Explain the importance of the volatile keyword in C++.

   • The volatile keyword is used to indicate that a variable may be changed by multiple threads or external factors, preventing compiler optimizations that might assume the variable remains unchanged.

4. What is the difference between struct and class in C++?

   • In a struct, members are public by default, while in a class, members are private by default. Additionally, class supports encapsulation and inheritance, while struct is primarily used for plain data structures.

5. Discuss the concept of function overloading and provide an example.

   • Function overloading allows multiple functions with the same name but different parameter lists. For example:

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

6. What is the difference between new and malloc() in C++?

   • new is an operator in C++ that allocates memory for an object and calls its constructor. malloc() is a function in C that allocates raw memory without calling any constructors.

7. Explain the purpose of the explicit keyword in C++.

   • The explicit keyword is used to prevent implicit type conversions, making constructors with a single parameter explicit in their usage.

8. How does the sizeof operator work in C++?

   • The sizeof operator returns the size, in bytes, of a variable or data type. For example, sizeof(int) returns the size of an integer.

9. Describe the purpose of the inline keyword.

   • The inline keyword suggests the compiler to insert the code of a function directly into the calling code, potentially improving performance by avoiding function call overhead.

10. What is a lambda expression in C++? Provide an example.

    • A lambda expression is an anonymous function. Example:

      auto sum = [](int a, int b) { return a + b; };
      int result = sum(3, 4); 

Object-Oriented Programming (OOP):

11. Explain the concept of inheritance in C++.

    • Inheritance allows a class to inherit properties and behaviors from another class. Example:

       class Base {
      public:
          int getData() { return data; }
      private:
          int data;
      };
      
      class Derived : public Base {
      // Derived has access to getData()
      };
      

12. What is polymorphism? How is it achieved in C++?

    • Polymorphism allows objects of different types to be treated as objects of a common type. It is achieved in C++ through function overloading and virtual functions.

13. Describe encapsulation and its advantages in C++.

    • Encapsulation is the bundling of data and the methods that operate on the data into a single unit (class). It helps in data hiding and protects the integrity of the data.

14. What is the difference between early binding and late binding?

    • Early binding (static binding) occurs at compile-time, while late binding (dynamic binding) occurs at runtime. Virtual functions enable late binding in C++.

15. Discuss the importance of the virtual keyword in C++.

    • The virtual keyword is used to declare virtual functions in base classes, allowing them to be overridden by derived classes. It enables polymorphic behavior.

16. How does the friend keyword work in C++?

    • The friend keyword allows a function or class to access private members of another class. It is often used for implementing non-member functions that need access to private members.

17. Explain the concept of an abstract class.

    • An abstract class is a class that cannot be instantiated and may have one or more pure virtual functions. It serves as a base class for other classes, providing a common interface.

18. What is multiple inheritance, and how is it implemented in C++?

    • Multiple inheritance allows a class to inherit from more than one base class. It is implemented in C++ by separating the base class names with commas in the class declaration.

19. Discuss the role of a destructor in C++.

    • A destructor is a special member function that is called when an object goes out of scope or is explicitly deleted. It is used to release resources and perform cleanup.

20. What is an interface in C++?

    • C++ does not have a specific interface keyword like some other languages. Interfaces are typically represented by abstract classes with pure virtual functions.

Pointers and Memory Management:

21. What is a pointer? How is it different from a reference?

    • A pointer is a variable that holds the memory address of another variable. A reference is an alias for a variable. Unlike pointers, references cannot be NULL and cannot be reseated to refer to another variable.

22. Explain the purpose of the nullptr keyword in C++.

    • nullptr is a keyword introduced in C++11 to represent a null pointer. It is recommended to use nullptr instead of NULL or 0 for better type safety.

23. Discuss the differences between delete and delete[] in C++.

    • delete is used to deallocate memory for a single object created using new, while delete[] is used to deallocate memory for an array of objects created using new[].

24. What is a smart pointer, and why is it used?

    • A smart pointer is a C++ object that acts like a pointer but provides additional features such as automatic memory management. Examples include std::shared_ptr and std::unique_ptr.

25. How does memory leak occur in C++? How can it be avoided?

    • Memory leaks occur when dynamically allocated memory is not deallocated. They can be avoided by properly using delete for each new and by using smart pointers.

26. Explain shallow copy and deep copy.

    • Shallow copy copies the values of the members, including pointers, but does not duplicate the dynamically allocated memory. Deep copy creates a new copy of the dynamically allocated memory.

27. What is the purpose of the const keyword when used with pointers?

    • When used with pointers, const can be used to indicate that the pointed-to data is constant (const int*) or that the pointer itself is constant (int* const).

28. Discuss the concept of a dangling pointer.

    • A dangling pointer is a pointer that points to memory that has been deallocated or is otherwise invalid. Dereferencing a dangling pointer can lead to undefined behavior.

29. How is dynamic memory allocation handled in C++?

    • Dynamic memory allocation is done using operators new and delete or malloc() and free(). It allows memory to be allocated at runtime and must be manually deallocated.

Templates and STL:

30. What are templates in C++? Provide an example.

    • Templates allow the creation of generic classes and functions. Example:

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

31. Explain the concept of template specialization.

    • Template specialization allows defining a specialized implementation for a specific data type. Example:

      template <>
      int add<int>(int a, int b) {
          return a * b;  // Specialized implementation for int
      }
       

32. Discuss the purpose of the Standard Template Library (STL).

    • The STL is a collection of template classes and functions in C++, providing generic algorithms, containers, and iterators. It simplifies complex data structures and algorithms.

33. What is the difference between a vector and a list in STL?

    • A vector is a dynamic array that allows fast random access, while a list is a doubly-linked list that allows efficient insertion and deletion at both ends.

34. How does the map container work in STL?

    • std::map is an associative container that stores key-value pairs in a sorted order based on the key. It uses a binary search tree (usually a red-black tree) for efficient lookups.

35. What is an iterator in C++?

    • An iterator is an object that points to an element in a container, allowing traversal and manipulation of container elements. Iterators provide a uniform way to access elements in different containers.

36. Explain the purpose of the algorithm header in STL.

    • The algorithm header provides a collection of template functions for common algorithms such as sorting, searching, and manipulating elements in containers.

37. Discuss the difference between std::vector and std::array.

    • std::vector is a dynamic array that can grow or shrink in size, while std::array is a fixed-size array with a fixed capacity determined at compile-time.

Exception Handling:

38. What is exception handling in C++?

    • Exception handling is a mechanism to handle runtime errors and unexpected situations. It involves try, catch, and throw keywords.

39. Explain the try, catch, and throw keywords.

    • try is used to enclose a block of code that might throw an exception. catch is used to handle exceptions, and throw is used to throw an exception.

40. Discuss the difference between runtime and compile-time errors.

    • Compile-time errors are detected by the compiler during the compilation process, while runtime errors occur during program execution. Exception handling is used to address runtime errors.

41. How is exception handling implemented in C++?

    • C++ uses a stack-based mechanism to propagate and handle exceptions. When an exception is thrown, the program unwinds the call stack until a matching catch block is found.

Advanced Topics:

42. What is the role of the volatile keyword in multithreading?

    • The volatile keyword indicates that a variable may be changed by multiple threads. It prevents the compiler from optimizing away reads and writes to the variable.

43. Explain the concept of move semantics in C++.

    • Move semantics involve efficiently transferring ownership of resources (such as memory) from one object to another without unnecessary copying. It is implemented using move constructors and move assignment operators.

44. Discuss the purpose of the override keyword.

    • The override keyword is used to indicate that a member function in a derived class is intended to override a virtual function in the base class. It helps catch errors when the intended override is missing.

45. What is the Rule of Three in C++?

    • The Rule of Three states that if a class defines any of the following three, it should define all three: destructor, copy constructor, and copy assignment operator. This ensures proper resource management.

46. What is the Rule of Five in C++?

    • The Rule of Five extends the Rule of Three to include move constructor and move assignment operator. If a class manages resources, it should define all five special member functions.

47. Explain the concept of CRTP (Curiously Recurring Template Pattern).

    • CRTP is a C++ programming pattern where a class template derives from a class that is a template specialization of itself. It is often used to implement static polymorphism.

48. Discuss the use of the auto keyword in C++.

    • The auto keyword allows the compiler to automatically deduce the type of a variable during compilation, reducing the need for explicit type declarations.

49. What is RAII (Resource Acquisition Is Initialization)?

    • RAII is a programming idiom in C++ where resource management is tied to object lifetime. Resources are acquired in the object's constructor and released in its destructor.

50. Explain the concept of type erasure in C++.

    • Type erasure is a technique to store objects of different types in a container while exposing a uniform interface. It is often used in scenarios where a single interface is needed for diverse types.