Mastering C++: 100 Interview Questions and Answers

Mastering C++: 100 Interview Questions and Answers

C++ Basics:

1. What is C++?
   • Answer: C++ is a high-level programming language derived from C, with features like object-oriented programming and templates.
2. Explain the difference between C and C++.
   • Answer: C++ adds features like classes, objects, and inheritance to C, making it an object-oriented language.
3. What is the difference between #include <iostream> and #include "iostream" in C++?
   • Answer: <iostream> is used for standard library headers, while "iostream" is used for user-defined headers.
4. What is a compiler in C++?
   • Answer: A compiler translates C++ code into machine code that a computer can execute.
5. What is an IDE, and name some C++ IDEs.
   • Answer: An Integrated Development Environment (IDE) is a software suite for coding. Some C++ IDEs include Visual Studio, Code::Blocks, and CLion.

Variables and Data Types:

6. How do you declare a variable in C++?
   • Answer: You declare a variable by specifying its type and name, e.g., int age;.
7. What is the difference between int and float data types?
   • Answer: int is for integer values, while float is for floating-point (decimal) values.
8. What is the sizeof operator used for in C++?
   • Answer: sizeof returns the size in bytes of a variable or data type.
9. Explain the purpose of the const keyword in C++.
   • Answer: const is used to make a variable or function parameter immutable (read-only).
10. What are the basic data types in C++?
    • Answer: Basic data types include int, float, double, char, and bool.

Operators and Expressions:

11. What is the difference between = and == in C++?
    • Answer: = is the assignment operator, while == is the equality operator used for comparisons.
12. Explain the concept of operator precedence in C++.
    • Answer: Operator precedence determines the order in which operators are evaluated in an expression. For example, multiplication (*) has higher precedence than addition (+).
13. What is the difference between pre-increment and post-increment operators (++i and i++)?
    • Answer: ++i is pre-increment (increments and then uses the value), while i++ is post-increment (uses the value and then increments).
14. What is the ternary conditional operator (?:) in C++?
    • Answer: It’s a shorthand for an if-else statement, used for simple conditional assignments.
15. Explain the concept of type casting in C++.
    • Answer: Type casting is the conversion of one data type to another, such as converting an int to a double.

Control Flow:

16. What is an if statement, and how is it used in C++?
    • Answer: An if statement is used for conditional execution. It executes a block of code if a specified condition is true.
17. What is a for loop in C++?
    • Answer: A for loop is used for iterating over a block of code a specific number of times.
18. Explain the purpose of the switch statement in C++.
    • Answer: switch is used to select one of many code blocks to be executed based on the value of an expression.
19. What is the difference between while and do-while loops in C++?
    • Answer: while checks the condition before executing the loop, while do-while checks it after, ensuring the loop runs at least once.
20. What is the purpose of the break and continue statements in C++?
    • Answer: break is used to exit a loop prematurely, and continue is used to skip the rest of the current iteration and continue with the next one.

Functions:

21. How do you declare and define a function in C++?
    • Answer: Declare the function’s prototype, define the function’s code, and then call it.
22. What is the difference between call by value and call by reference in C++?
    • Answer: Call by value passes a copy of the argument to the function, while call by reference passes a reference to the original argument.
23. What is function overloading in C++?
    • Answer: Function overloading allows you to define multiple functions with the same name but different parameter lists.
24. Explain the concept of recursion in C++.
    • Answer: Recursion is a function calling itself. It’s often used to solve problems that can be broken down into smaller, similar subproblems.
25. What is a default argument in a C++ function?
    • Answer: A default argument is a value assigned to a function parameter that is used if the caller doesn’t provide an argument for that parameter.

Arrays and Pointers:

26. How do you declare and initialize an array in C++?
    • Answer: Declare an array with a specified size and initialize it with values in curly braces {}.
27. What is a pointer in C++?
    • Answer: A pointer is a variable that stores the memory address of another variable.
28. How do you allocate and deallocate memory using new and delete in C++?
    • Answer: new is used to allocate memory for an object, and delete is used to deallocate it.
29. Explain the difference between an array and a pointer in C++.
    • Answer: An array is a collection of elements with the same data type, while a pointer is a variable that stores a memory address.
30. What is pointer arithmetic, and how is it used in C++?
    • Answer: Pointer arithmetic involves performing arithmetic operations on pointers to navigate and manipulate memory.

Object-Oriented Programming (OOP):

31. What is a class in C++?
    • Answer: A class is a blueprint for creating objects with attributes and methods.
32. What is an object in C++?
    • Answer: An object is an instance of a class, representing a specific entity.
33. What is encapsulation in OOP, and why is it important?
    • Answer: Encapsulation is the concept of bundling data and methods that operate on that data within a single unit (class). It promotes data hiding and security.
34. What is inheritance in C++, and how is it implemented?
    • Answer: Inheritance allows a class to inherit attributes and methods from another class. It’s implemented using the : operator.
35. What is polymorphism in OOP, and how is it achieved in C++?
    • Answer: Polymorphism allows objects of different classes to be treated as objects of a common base class. It’s achieved through function overriding and virtual functions.

Constructors and Destructors:

36. What is a constructor, and what is its purpose in C++?
    • Answer: A constructor is a special member function used for initializing objects. It’s called automatically when an object is created.
37. Explain the difference between a parameterized constructor and a default constructor.
    • Answer: A parameterized constructor accepts arguments, while a default constructor has no arguments.
38. What is a destructor in C++, and what is its purpose?
    • Answer: A destructor is a special member function used to clean up resources when an object goes out of scope.
39. How do you create a copy constructor in C++?
    • Answer: A copy constructor is created by defining a constructor that takes an object of the same class as its parameter.
40. What is the difference between a constructor and a member function in a C++ class?
    • Answer: A constructor is used to initialize objects when they are created, while a member function is called to perform specific operations on objects.

Operator Overloading:

41. What is operator overloading in C++, and why is it used?
    • Answer: Operator overloading allows you to define custom behaviors for operators when applied to user-defined classes or types.
42. Give an example of operator overloading in C++.
    • Answer: Overloading the + operator to add two objects of a custom class.
43. Explain the difference between unary and binary operators in C++.
    • Answer: Unary operators work on a single operand, while binary operators work on two operands.
44. How do you overload the << operator for output stream in C++?
    • Answer: Overload the << operator as a friend function in your class to customize output.
45. What is the rule of three (or rule of five) in C++?
    • Answer: The rule of three (or five) states that if a class defines a destructor, copy constructor, or copy assignment operator, it should define all three (or five) to manage resources correctly.

STL (Standard Template Library):

46. What is the STL in C++, and what are its main components?
    • Answer: The STL is a collection of C++ template classes to provide general-purpose classes and functions with templates. Its main components include containers, algorithms, and iterators.
47. What is a vector in the C++ STL?
    • Answer: A vector is a dynamic array that can grow or shrink in size, providing efficient random access and insertion/removal at the end.
48. Explain the difference between std::vector and std::array in C++ STL.
    • Answer: std::vector is a dynamic array with a variable size, while std::array is a fixed-size array.
49. What is an iterator in the C++ STL?
    • Answer: An iterator is an object used to traverse and manipulate elements of a container, such as a vector or list.
50. What is the purpose of the std::map container in C++ STL?
    • Answer: std::map is an associative container that stores key-value pairs in a sorted order, allowing fast lookups by key.

Memory Management:

51. What is dynamic memory allocation in C++?
    • Answer: Dynamic memory allocation involves allocating and deallocating memory during program execution using functions like new and delete.
52. How do you allocate memory for an array dynamically using new in C++?
    • Answer: Use new to allocate memory, like int* arr = new int[5];.
53. What is a memory leak in C++, and how can you avoid it?
    • Answer: A memory leak occurs when a program fails to deallocate memory, causing memory consumption to grow. To avoid it, always deallocate dynamically allocated memory using delete.
54. Explain the purpose of the malloc() and free() functions in C++.
    • Answer: malloc() is used to allocate memory, and free() is used to deallocate memory in C, whereas in C++, it’s more common to use new and delete.
55. What is RAII (Resource Acquisition Is Initialization) in C++?
    • Answer: RAII is a C++ programming idiom where resource management (e.g., memory allocation) is tied to the lifetime of an object. Resources are automatically released when the object goes out of scope.

File Handling:

56. How do you open and close a file in C++?
    • Answer: Use std::ifstream or std::ofstream to open a file for reading or writing, respectively, and close it with close().
57. What is the purpose of the std::fstream class in C++?
    • Answer: std::fstream is a class used for file input and output, allowing both reading and writing operations on files.
58. How do you read data from a file in C++?
    • Answer: Use >> or getline() to read data from a file, depending on the data format.
59. What is the difference between text mode and binary mode when opening a file in C++?
    • Answer: Text mode is for reading and writing text files, while binary mode is for reading and writing binary files. In binary mode, data is read or written as-is, without any character encoding conversions.
60. How do you check if a file exists in C++ before opening it?
    • Answer: You can use the std::ifstream constructor with the file’s name to check if it exists. If the file doesn’t exist, the stream will be in a failed state.

Exception Handling:

61. What is exception handling in C++, and why is it used?
    • Answer: Exception handling is a mechanism to handle runtime errors gracefully by using try, catch, and throw.
62. Explain the use of the try, catch, and throw keywords in C++.
    • Answer: try is used to enclose code that might raise an exception, catch is used to handle exceptions, and throw is used to raise custom exceptions.
63. What is the purpose of the std::exception class in C++?
    • Answer: std::exception is a base class for all standard C++ exceptions. It provides a common interface for handling exceptions.
64. What is the difference between throw and throw with no argument in C++?
    • Answer: throw with no argument rethrows the current exception, while throw with an argument throws a new exception of the specified type.
65. What is stack unwinding in C++ exception handling?
    • Answer: Stack unwinding is the process of deallocating local objects and returning control to the appropriate catch block when an exception is thrown.

Templates and Generic Programming:

66. What is a template in C++?
    • Answer: A template is a blueprint for creating generic classes or functions that can work with different data types.
67. Explain the difference between function templates and class templates in C++.
    • Answer: Function templates allow you to create generic functions, while class templates allow you to create generic classes.
68. What is specialization in C++ template programming?
    • Answer: Template specialization allows you to provide a specific implementation for a given data type when using a generic template.
69. How do you define a function template in C++?
    • Answer: Use the template keyword followed by the template parameter list, and then define the function as you would normally.
70. What is type inference in C++ template programming?
    • Answer: Type inference allows the compiler to deduce the template argument types automatically based on the function arguments.

STL Containers:

71. What is the purpose of the std::vector container in C++ STL?
    • Answer: std::vector is a dynamic array that can grow or shrink, providing efficient random access and dynamic sizing.
72. What is the std::map container in C++ STL used for?
    • Answer: std::map is an associative container that stores key-value pairs in a sorted order for fast lookups by key.
73. Explain the purpose of the std::set container in C++ STL.
    • Answer: std::set is an ordered container that stores unique elements, making it useful for maintaining a sorted collection without duplicates.
74. What is the std::list container in C++ STL, and when is it used?
    • Answer: std::list is a doubly-linked list container, often used when frequent insertion and deletion of elements are required.
75. What is the std::deque container in C++ STL, and how does it differ from std::vector?
    • Answer: std::deque is a double-ended queue that allows efficient insertion and removal at both ends. It differs from std::vector in terms of data structure and usage.

STL Algorithms:

76. What are STL algorithms in C++, and why are they important?
    • Answer: STL algorithms are a set of pre-defined functions for common operations on containers, promoting code reuse and readability.
77. Explain the purpose of the std::sort() algorithm in C++.
    • Answer: std::sort() is used to sort elements in a container in ascending order.
78. What is the difference between std::find() and std::find_if() in C++ STL?
    • Answer: std::find() is used to find an element with a specific value, while std::find_if() is used to find an element that satisfies a given condition.
79. What is the std::accumulate() algorithm in C++ used for?
    • Answer: std::accumulate() is used to compute the sum (or product) of elements in a range.
80. Explain the purpose of the std::transform() algorithm in C++.
    • Answer: std::transform() applies a specified operation to each element in a range and stores the results in another container.

Smart Pointers:

81. What are smart pointers in C++, and why are they used?
    • Answer: Smart pointers are objects that manage the memory of dynamically allocated objects, helping to prevent memory leaks and manage resources.
82. What is the difference between std::shared_ptr and std::unique_ptr in C++?
    • Answer: std::shared_ptr allows multiple pointers to share ownership of an object, while std::unique_ptr has sole ownership.
83. Explain the purpose of the std::weak_ptr in C++ smart pointers.
    • Answer: std::weak_ptr is used for non-intrusive cyclic references in cases where std::shared_ptr could lead to circular references.
84. How do you create a smart pointer in C++?
    • Answer: Use std::shared_ptr, std::unique_ptr, or std::weak_ptr with std::make_shared() or std::make_unique() for allocation.
85. What is the purpose of std::make_shared() in C++ smart pointers?
    • Answer: std::make_shared() is a helper function that creates a std::shared_ptr with better memory management than using new directly.

Concurrency and Multithreading:

86. What is multithreading in C++, and why is it used?
    • Answer: Multithreading is a technique that allows a program to run multiple threads concurrently, improving performance and responsiveness.
87. Explain the difference between a thread and a process in C++.
    • Answer: A process is a separate instance of a program, while a thread is a smaller unit of a process that can run concurrently.
88. What is the purpose of the std::thread class in C++?
    • Answer: std::thread is used to create and manage threads in C++, allowing for concurrent execution of code.
89. How do you synchronize access to shared resources in multithreaded C++ programs?
    • Answer: Synchronization can be achieved using mutexes (std::mutex) and other synchronization primitives like condition variables.
90. What is a race condition, and how can it be avoided in multithreaded C++ programs?
    • Answer: A race condition occurs when multiple threads access shared data concurrently, leading to unpredictable results. It can be avoided by using proper synchronization techniques like mutexes.

Advanced C++ Topics:

91. What is the purpose of the volatile keyword in C++?
    • Answer: volatile is used to indicate that a variable may be modified by external factors and should not be optimized by the compiler.
92. What is a lambda expression in C++, and how is it used?
    • Answer: A lambda expression is an anonymous function that can capture and use local variables. It’s often used for concise callbacks and custom sorting functions.
93. Explain the purpose of the C++ Standard Library (STL).
    • Answer: The STL is a collection of C++ template classes and functions that provide common data structures and algorithms, promoting code reuse and portability.
94. What is RAII (Resource Acquisition Is Initialization) in C++?
    • Answer: RAII is a C++ programming idiom where resource management (e.g., memory allocation) is tied to the lifetime of an object. Resources are automatically released when the object goes out of scope.
95. What is the purpose of the const keyword in C++?
    • Answer: const is used to indicate that a variable or object cannot be modified after it’s been initialized.
96. Explain the difference between a reference and a pointer in C++.
    • Answer: A reference is an alias for an existing object, while a pointer is a separate variable that stores an address.
97. What is the purpose of the inline keyword in C++?
    • Answer: inline suggests that the compiler should perform inline expansion of a function, replacing the function call with the function code.
98. What is the rule of three (or rule of five) in C++?
    • Answer: The rule of three (or five) states that if a class defines a destructor, copy constructor, or copy assignment operator, it should define all three (or five) to manage resources correctly.
99. Explain the concept of template specialization in C++.
    • Answer: Template specialization allows you to provide a specific implementation for a given data type when using a generic template.
100. What is the purpose of the std::move() function in C++? – Answer: std::move() is used to cast an lvalue to an rvalue, allowing for efficient move semantics and avoiding unnecessary copying.