Questions and Answers of C++ | C++ Interview questions

1. What is C++?

Answer: C++ is an object-oriented programming language created by Bjarne Stroustrup. It was released in 1985. C++ is a superset of C with the major addition of classes in C language. It is a versatile programming language that extends C with features like classes, objects, and inheritance, facilitating both procedural and object-oriented programming.

2. Who was the creator of C++?

Answer: Bjarne Stroustrup.

3. Which programming language’s unsatisfactory performance led to the discovery of C++?

Answer: C++ was discovered in order to cope with the disadvantages of C.

4. What is array?

Answer: An array is a collection of similar data elements stored at contiguous memory locations. This data type is useful when a group of elements are to be represented by a common name. An array is used to store a group of data items that belong to the same data type.

An array is a group of elements that share a common name, and is differentiated from one another by their positions within the array. An array is also defined as a collection of homogeneous data.

5. How is object-oriented programming different from procedural programming?

Ans. In object-oriented programming, the entire program is divided into smaller units called objects and works on the bottom-up approach. Whereas, in procedural programming, the entire program is divided into smaller units called functions and works on the top-down approach.

In a nutshell, procedural programming does not provide any data security whereas, in contrast to it, object-oriented programming ensures data security with the help of access specifiers, proving to be more secure and efficient.

C++ supports object-oriented programming whereas C supports procedural programming.

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

Answer: C++ is an extension of C with additional features like classes, objects, inheritance, polymorphism, and templates, which are not available in C. Additionally, C++ supports function overloading and namespaces, which are not present in C.

7. What is a class?

Answer: A class is a template used for creating objects. It defines attributes (data members) and behaviors (member functions) that the objects of the class will have.

The class is a user-defined data type. The class is declared with the keyword class. The class contains the data members, and member functions whose access is defined by the three modifiers are private, public and protected.

8. What is an object?

Answer: An object is an instance of a class. Since a class is a user-defined data type so an object can also be called a variable of that data type. A class provides a blueprint for objects. So, we can create object from a class. We can create N number of objects from a class. Object depicts a thing or idea that exists in reality.

9. What is Function? Explain types of Functions.

Answer: A function is a block of codes or a group of statements that together perform a specific task. Every C++ program must have at least one function, which is the main() function. We can divide our code into separate functions. A program can have any number of functions. The main() function is the starting point of a program. 

A function is a block of code which only runs when it is called. We can pass data, known as parameters, into a function. Functions are used to perform certain actions, and they are important for reusing code: Define the code once, and use it many times.

There are two types of functions in C++

• Built-in functions
• User-defined functions

Built-in Functions:

Built-in functions are also called “Library Functions”. These are functions that are already present in C++; their definitions are already provided in the header files. The compiler picks the definition from header files and uses them in the program.

Built-in Function gives us an edge as we can directly use them without defining them whereas in the user-defined function we have to declare and define a function before using them. For Example: sqrt(), setw(), strcat(), etc.

User Defined Function:

User defined functions are defined by the user.  C++ allows us to create functions according to our need. If there is no appropriate library function for specific requirement, we can create our own function to perform the desired operation. Once a function is defined, we can easily call and use the function whenever it requires. User-defined functions are user-defined blocks of code specially customized to reduce the complexity of big programs.

10. What is a constructor?

Answer: A constructor is a method of a class that is automatically called when an object of that class is created. It is used to initialize the object’s data members. Class name and method name are the same in a constructor. And no return type is used for constructors.

11. What is a destructor?

Answer: A constructor is automatically called when an object is first created. Similarly, when an object is destroyed a function called destructor automatically gets called. A destructor has the same name as the constructor (which is the same as the class name) but is preceded by a tilde (~).

12. What are the similarities between constructors and destructors?

Ans. Both constructors and destructors in C++ need to be declared within the class with the same name as that of the class. Even if they aren’t declared inside the class, they exist by default but in this case, we can use them only to allocate and deallocate memory from the objects of a class, whenever the object is declared or deleted.

13. What is inheritance?

Answer: Inheritance is a mechanism in C++ by which a class can inherit properties and behaviors from another class. The class that inherits is called the derived class, and the class from which it inherits is called the base class.

14. What is polymorphism?

Answer: Polymorphism in simple means having many forms. Its behavior is different in different situations.

Polymorphism is the ability of a function or operator to behave differently based on the object that it is operating on. It can be achieved in C++ through function overloading, function overriding, and using virtual functions.

15. What is encapsulation?

Answer: Encapsulation is the bundling of data (attributes) and functions (methods) that operate on the data into a single unit (class). It helps in hiding the internal implementation details of a class from the outside world. It simply means wrapping up the data in a single unit.

16. What do you mean by abstraction in C++?

Answer: Abstraction is the process of showing the essential details to the user and hiding the details which we don’t want to show to the user or hiding the details which are irrelevant to a particular user.

17. How would you establish the relationship between abstraction and encapsulation?

Answer: Data abstraction refers to representing only the important features of the real-world object in the C++ program. This entire process does not include any explanation and background details of the code. Abstraction is implemented with the help of classes and objects, whereas, data encapsulation is the most significant feature of a class.

Data encapsulation in C++ refers to the wrapping up of data members and member functions that operate on the data as a single unit, called the class. Encapsulation prevents free access to the members of the class.

18. What is function overloading?

Answer: Function overloading is a feature of C++ that allows a function to have multiple definitions with the same name but different parameter lists.

19. What is operator overloading?

Answer: Operator overloading is a feature of C++. Operator overloading allows us to redefine the behavior of operators like +, -, etc., for user-defined data types. Operator Overloading is a very essential element to perform the operations on user-defined data types.  By operator overloading we can modify the default meaning to the operators like +, -, *, /, <=, etc.

20. Explain function overloading and function overriding.

Answer: Function overloading is having multiple functions with the same name but different parameter lists in the same scope. Function overriding occurs when a derived class provides its own implementation for a virtual function declared in a base class.

21. What are the advantages of C++?

Answer: C++ doesn’t only maintain all aspects from C language, it also simplifies memory management and adds several features like:

• C++ is a highly portable language means that the software developed using C++ language can run on any platform.
• C++ is an object-oriented programming language which includes the concepts such as classes, objects, inheritance, polymorphism, abstraction.
• C++ has the concept of inheritance. Through inheritance, one can eliminate the redundant code and can reuse the existing classes.
• Data hiding helps the programmer to build secure programs so that the program cannot be attacked by the invaders.
• Message passing is a technique used for communication between the objects
  C++ contains a rich function library.

22. How many keywords do C++ languages support?

Answer: There are 52 keywords in the C++ language.

23. What is the difference between cin and gets() functions?

Answer: cin cannot accept string with space gets() function is used to accept a string of characters including whitespace.

24. What are the various OOPs concepts in C++?

Answer: The various OOPS concepts in C++ are:

Class: A class is a template used for creating objects. It defines attributes (data members) and behaviors (member functions) that the objects of the class will have.

The class is a user-defined data type which defines its properties and its functions.

Object: An object is a run-time entity. An object is the instance of the class. An object can represent a person, place or any other item. An object can operate on both data members and member functions.

Inheritance: Inheritance is a technique of deriving a new class from the old class. The old class is known as the base class, and the new class is known as derived class. Inheritance provides reusability. Reusability means that one can use the functionalities of the existing class. It eliminates the redundancy of code.

Encapsulation: Encapsulation is a technique of wrapping the data members and member functions in a single unit. It binds the data within a class, and no outside method can access the data. If the data member is private, then the member function can only access the data.

Abstraction: Abstraction is a technique of showing only essential details without representing the implementation details. If the members are defined with a public keyword, then the members are accessible outside also. If the members are defined with a private keyword, then the members are not accessible by the outside methods.

Polymorphism: Polymorphism means multiple forms. Polymorphism means having more than one function with the same name but with different functionalities. Polymorphism is of two types:

• Static polymorphism is also known as early binding.
• Dynamic polymorphism is also known as late binding.

25. Define namespace in C++?

Answer:

• The namespace is a logical division of the code which is designed to stop the naming conflict.
• The namespace defines the scope where the identifiers such as variables, class, functions are declared.
• The main purpose of using namespace in C++ is to remove the ambiguity. Ambiquity occurs when the different task occurs with the same name.
• For example: if there are two functions exist with the same name such as add(). In order to prevent this ambiguity, the namespace is used. Functions are declared in different namespaces.
• C++ consists of a standard namespace, i.e., std which contains inbuilt classes and functions. So, by using the statement “using namespace std;” includes the namespace “std” in our program.

26. What are the C++ access specifiers?

Answer: The access specifiers are used to define how to functions and variables can be accessed outside the class. There are three types of access specifiers:

• Private: Functions and variables declared as private can be accessed only within the same class, and they cannot be accessed outside the class they are declared.
• Public: Functions and variables declared under public can be accessed from anywhere.
• Protected: Functions and variables declared as protected cannot be accessed outside the class except a child class. This specifier is generally used in inheritance.

27. What is Object Oriented Programming (OOP)?

Answer: OOP is a methodology or paradigm that provides many concepts. The basic concepts of Object-Oriented Programming are given below:

Classes and Objects: Classes are used to specify the structure of the data. They define the data type. We can create any number of objects from a class. Objects are the instances of classes.

Encapsulation: Encapsulation is a mechanism which binds the data and associated operations together and thus hides the data from the outside world. Encapsulation is also known as data hiding. In C++, It is achieved using the access specifiers, i.e., public, private and protected.

Abstraction: Abstraction is used to hide the internal implementations and show only the necessary details to the outer world. Data abstraction is implemented using interfaces and abstract classes in C++.

Some people confused about Encapsulation and abstraction, but they both are different.

Inheritance: Inheritance is used to inherit the property of one class into another class. It facilitates you to define one class in term of another class.

28. What is the difference between C and C++

Answer: The main difference between C and C++ are provided in the table below:

C	C++
C is a procedure-oriented programming language.	C++ is an object-oriented programming language.
C does not support data hiding.	Data is hidden by encapsulation to ensure that data structures and operators are used as intended.
C is a subset of C++	C++ is a superset of C.
Function and operator overloading are not supported in C	Function and operator overloading is supported in C++
Namespace features are not present in C	Namespace is used by C++, which avoids name collisions.
Functions cannot be defined inside structures.	Functions can be defined inside structures.
calloc() and malloc() functions are used for memory allocation and free() function is used for memory deallocation.	new operator is used for memory allocation and deletes operator is used for memory deallocation.