Top Object-oriented Programming Interview Questions in C# and C++

To land lucrative offers at top companies, you must master Object-oriented programming interview questions in C# and C++. Being skilled in C# and C++ is essential if the company you're applying to primarily uses these programming languages. Object-oriented programming interview questions on C# and C++ are crucial during technical interviews due to their importance in the tech field.

C# is a statically-typed, object-oriented, generic, and component-oriented programming language. If you are inclined towards web or game development, you can build dynamic websites and applications using C#. In this article, we will provide you with a comprehensive list of questions to practice that will help you assess your C# tech interview prep. 

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Here's what we'll cover:

• Most Commonly Asked Object-oriented Programming Interview Questions in C#
• Advanced Object-oriented Programming Interview Questions in C#
• C++ Object-oriented Programming Interview Questions for Practice
• FAQs on Object-oriented Programming Interview Questions in C#

Most Commonly Asked Object-oriented Programming Interview Questions in C#

You must go through the following C# object-oriented programming interview questions to brush up on the basic OOP concepts in context with C#.

Q1. How is an Interface different from an Abstract Class?

The key differences between an interface and an abstract class are:

Q2. What happens if you have conflicting method names for the inherited interfaces?

This is one of the most common object-oriented programming interview questions C#. If you have conflicting method names, you will not be able to independently implement their body in the same class due to the same name and signature. To avoid confusion, you will have to use the interface name before the method name.

Q3. What is polymorphism in C#?

Polymorphism refers to having many forms. In OOP, polymorphism is the ability of different types of objects to provide a unique interface for different implementations of methods. The two types of polymorphism in C# are:

• Compile-time polymorphism: It is also called static or early binding, and is achieved by method overloading and operator overloading in C#. 
• Runtime polymorphism: It is also called dynamic or late binding, and it is achieved by method overriding. 

Q4. How is a method overloaded in C#?

Method overloading or compile-time polymorphism is when two or more methods have the same name but different parameters. You can create a method with the same name but with a different signature at compile time. The different ways of overloading methods are by changing:  

• The number of parameters in two methods.
• The order of the parameters of methods.
• The data types of the parameters of methods.

Q5. What are the different types of Access Modifiers in C#?

Access modifiers are keywords that specify the declared accessibility of a type or a member. There are five types of access modifiers: 

• Public: There are no restrictions on accessing public members.
• Private: There is limited access as the code is only accessible within the same class. 
• Protected: The access is limited to the within-class or in any class inherited from the class.
• Internal: The access is limited to the classes defined by the current project but not from another assembly. There are two types: protected internal and private protected.

Q6. What do you understand about a virtual method in C#?

A method that can be redefined in a derived class is called a virtual method. In C#, it can be implemented on the base and derived classes. It is used when more functionality is needed in the derived class. You can create a virtual method in the base class using the virtual keyword. This method is overridden in the derived class with the help of the override keyword.

Q7. What is encapsulation?

Encapsulation is one of the key features of C# and is often a part of object-oriented programming interview questions C#. It is the process of enclosing one or more items in a physical or logical package. In OOP methodology, encapsulation prevents access to implementation details.

Q8. What is inheritance? What are the different types of inheritances supported in C#?

You can define a class in terms of another class via inheritance, making it easier to create and maintain an application. Inheritance allows reuse of the code functionality and speeds up implementation time. 

For instance, if you create a class, you need not write the new data members and member functions completely. You can simply designate that the new class should inherit an existing class's members and member functions. The existing class is the base class, and the new class is the derived class.

C# supports the following types of inheritances:

• Single inheritance 
• Hierarchical inheritance
• Multilevel inheritance
• Multiple inheritances

Q9. What is the use of Interfaces in C#?

Interfaces are used in C# for the following reasons:

• Extensibility
• Loose coupling
• Implementation Hiding
• Accessing objects using interfaces

Q10. What are implicit and explicit interface implementations?

An implicit interface implementation is the most regular way to implement members of an interface. You implement implicitly and do not specify the interface name of the members.  

Explicit interface implementation requires you to specify the interface name of the members. Explicitly implemented members can be accessed through an Interface instance and not by using a class instance. 

Q11. What are the different types of design patterns?

You should be prepared to elucidate each of the following three types of design patterns while answering object-oriented programming interview questions C#:

• Creational patterns deal with the creation of objects and classes.
• Structural patterns that deal with class and object composition.
• Behavioral patterns that deal with class and object communication.

Q12. Enumerate differences between abstraction and encapsulation.

Following are the key differences between encapsulation and abstraction: 

• Abstraction for hiding the unwanted data and providing only relevant data, while encapsulation hides the code and data into a single unit to provide protection from the outer world.
• Abstract classes and interfaces are used to implement abstraction. Contrastingly, encapsulation can be implemented using access modifiers (private, protected, and public).
• Abstraction solves an issue at the design level, whereas encapsulation solves it at the implementation level.

Don’t forget to check the top C# Coding Interview Questions and Answers you need to prepare

Advanced Object-oriented Programming Interview Questions in C#

If you are applying for senior software developer positions, you should be familiar with advanced OOP concepts and be prepared for scenario-based, object-oriented programming interview questions in C#.

1. What are the different types of constructors in C#? Mention the significance of each.
2. How is a static class different from a singleton instance?
3. Why can abstract classes not be instantiated?
4. What is operator overloading?
5. Is it possible to inherit Enum in C#?
6. Can you achieve method extension using Interface?
7. What is ReadOnly? How is it different from Static ReadOnly?
8. How would you call the base class constructor from the derived class in C#?
9. How would you catch multiple exceptions at once in C#?
10. How would you prevent a class from overriding in C#?
11. When would you use a struct instead of a class?
12. What is the significance of cohesion in OOP?
13. State differences between coupling and cohesion in C#?
14. How would you call a getter or setter in C#?
15. How would you explain monads to a non-programmer?

C++ Object-oriented Programming Interview Questions

C# and C++ are object-oriented programming languages with similar code. While C# is comparatively newer, C++ has been famous for many decades. Preparing object-oriented programming C++ interview questions can help you stand out from the competitors. 

1. What are the different types of inheritances supported by C++?
2. What storage classes does C++ support? 
3. What are constructors and destructors?
4. How is mixing different from inheritance?
5. How do mixins differ from Policy-Oriented Design?
6. What is dynamic binding in C++?
7. What do you understand about enumerated constants in C++?
8. What is an asymptotic notation in C++?

Learn about C++ STL container fundamentals in detail here.

This completes our list of the most anticipated object-oriented programming interview questions on C++ and C#. In addition to these questions, you must practice mock interviews to nail the most challenging technical interviews. 

FAQs on Object-oriented Programming Interview Questions in C#

Q1. What are the important concepts for object-oriented programming interview questions in C#?

You should thoroughly prepare OOPs concepts, including classes, objects, data hiding, overloading, encapsulation, abstraction, polymorphism, and inheritance, to nail the most challenging object-oriented programming interview questions in C#.

Q2. Which companies put up object-oriented programming interview questions in C#?

Accenture, Google, Delivery Hero, Wipro, Infosys, HCL, TCs, Microsoft, Stack Overflow, Intuit, and Trustpilot are amongst the top tech companies that use C# in their tech stacks. You should be prepared for object-oriented programming interview questions C# if you are applying for software engineering roles at any of these companies. 

Q3. How should I prepare for C# object-oriented programming interview questions?

To nail the technical interview rounds at FAANG+ companies, you should begin by studying the basic and advanced concepts of C#. Once you know the crucial concepts, start practicing the most anticipated C# object-oriented programming interview questions. You must go through coding problems to improve your speed and accuracy. Finally, enroll in mock interviews to get familiar with the actual interview environment and receive feedback from hiring managers who are closely acquainted with the FAANG companies' interview processes.

Q4. How is object-oriented programming different from procedural?

Procedural programming is based on a modular approach wherein larger programs are broken into procedures. A procedure is a set of instructions executed one after another. Contrastingly, OOP is based upon objects, and an object contains various elements (methods and variables). 

You can specify the scope of data using access modifiers in OOP, but they are not used in procedural programming. Thus, procedural programming allows access to the entire data anywhere in the program.

Q5. Which language is better for coding interview rounds: C++ or C#?

C++ code is faster than C# code, and thus it is a better option for applications where performance is important. However, if you are a beginner planning to prepare any particular language for coding interview rounds, you should opt for the language mentioned in the job description or the one that is easier to learn. Experts suggest that C# is easier and quicker to learn. 

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