10 C# Interview Questions (With Example Answers)
Updated 16 November 2023
C# is a programming language used widely across various operating systems. It is a versatile programming language that is supported across platforms. It is an important skill to have to land a good job in the software testing industry. If you appear for a C# interview, you will likely encounter technical questions that will require extensive conceptual and practical knowledge to answer. Having some idea of what these questions could be will make you feel confident and prepared for your C# interview. In this article, we list 10 common C# interview questions and sample answers to help you prepare for your interview.
C# interview questions with sample answers
Here are some common C# interview questions you may be asked in your interview:
1. What are the different types of classes in C#?
The interviewer may ask this question to test your knowledge of OOP basics. To answer this question well, be direct and explain the four types briefly. The interviewer will ask a follow-up question if they want you to explain any of the types in more detail.
Example: “There are four different types of classes in C#. The first one is 'partial class'. This class allows its members to be divided or shared with multiple .cs files. It is denoted by the keyword ‘Partial'. The second class is the 'sealed class'. It is not possible to inherit this class. To access the members of this class, a user needs to create the object of the class. This class is denoted by the keyword ‘Sealed'. The third one is 'abstract class'. It is not possible to instantiate the object of this class. It is only possible to inherit this class. This class must contain at least one method. It is denoted by the keyword ‘abstract'. The fourth type is 'static class'. Inheritance is not allowed in this class. The members of this class are always static. This class is denoted by the keyword ‘static'. This keyword instructs the compiler to check for any instances of the static class, including any accidental instances.”
2. What is managed and unmanaged code?
This question is usually asked in the interviews to see if the candidate understands the compilation and execution of the code. The interviewer is trying to assess whether you can only write the code or understand its back-end. To answer this question, highlight the technical differences between the two types of code to effectively put across your knowledge of the core programming terms.
Example: “Managed code is any code that is executed by CLR (Common Language Runtime). It is called ‘managed code' because of the .Net framework, which uses the garbage collector internally to clear up unused memory. ‘__Unmanaged code' is any code that is executed by the application runtime of any other framework apart from .Net. The application runtime will take care of operations such as security, memory and other performance operations.”
3. What is a class and an object?
This is again a question that tests your basics of OOP. While answering this question, briefly explain both the concepts. It is also a good idea to share a simple real-world example to highlight the depth of your understanding.
Example: “A ‘Class' is an encapsulation of methods and properties that are used to represent an entity in real-time. Class brings all of the instances together in a single unit. An ‘Object' is an instance of a Class or a block of allocated memory that can be stored in the form of Variables, Array or a Collection.”
4. What is the difference between virtual method and abstract method?
This question tests the candidate's knowledge about method implementation in C#. Briefly explain both the methods and highlight their differences. You can expect a few follow-up questions on 'default implementation' or 'override keyword'.
Example: “A Virtual method must always have a default implementation. An Abstract method does not have an implementation. An override keyword is not necessary here, though it can be used.”
5. Explain namespaces in C#.
This is one of the most basic questions you can expect in a C# interview. This makes answering this question correctly that much more important. While answering, briefly explain the concept and share an example to showcase your knowledge.
Example: “Namespaces are used to organise large code projects. “System” is the most widely-used namespace in C#.”
6. Explain polymorphism.
This is a concept-based question that will help the interviewer understand the depth of your knowledge. Briefly explain the concept and also touch upon the different types. Giving simple code-based examples will demonstrate your understanding effectively.
Example: “In programming, polymorphism means the same method but different implementations. It contains two types, Compile-time and Runtime. Compile-time polymorphism is accomplished by operator overloading. Runtime polymorphism is accomplished by overriding. An example would be: a class has a method Void Add(), polymorphism is accomplished by Overloading the method, that is, void Add(int a, int b), void Add(int add) are all overloaded methods.”
7. How is exception handling implemented in C#?
With this question, the interviewer is trying to assess if you understand the different exception handling techniques. These techniques ensure the program runs smoothly and any issues that happen during the execution are handled and don't prove fatal. To answer this question, list all four keywords used in C# and explain each one briefly.
Example: “Exception handling is done using four keywords in C#. The first keyword is 'try'. This keyword contains a block of code that checks an exception. The second is 'catch'. It is a program that catches an exception with the help of an exception handler. The third one is 'finally'. It is a block of code written to execute even if an exception is not caught. The last is 'throw'. It throws an exception when a problem occurs.”
8. What are boxing and unboxing?
This is a technical question that allows the interviewer to test your knowledge of advanced concepts. To answer this well, briefly explain both concepts and be technical in the language you use.
Example: “Converting a value type to reference type is called ‘Boxing'. Explicit conversion of the same reference type that is created by boxing back to value type is called ‘Unboxing'.”
9. What is an array used for?
The ability to manipulate the storage of variables in a program is an essential skill for a programmer. This question tests this skill and helps the interviewer understand if the candidate understands the basics well. It is best to answer this question directly. Keep in mind you may be asked a few follow-up questions on this topic.
Example: “An array is used to store multiple variables of the same type and is a collection of variables stored in a contiguous memory location.”
10. What are the basic string operations?
This question helps the interviewer understand the candidate's knowledge about the different data types and the operations that can be performed on them. A similar kind of question may be asked about other data types as well. To answer this question, name the different operations and you can explain these in detail if asked to in a follow-up question.
Example: “The basic string operations are Concatenate, Search, Modify and Compare.”
Tips to prepare for your C# interview
Here are some tips to help you prepare for your C# interview:
Improve your coding skills
If you want to do well in your interview, you should review C# coding to increase your familiarity with it. C# is vast and it may not be easy to review everything, but it may be helpful to take a few online quizzes. The categories you must review are:
Principles of OOP
Abstract vs encapsulation
Shadowing and overriding
Types of polymorphism in C#
Research the role
Research the role and the company you are interviewing for to have an accurate idea of the work you will be doing. Study all requirements to ensure you can confidently fill the role. Understanding the role well helps you anticipate the questions that you may be asked in an interview.
Related: How to Prepare for a Job Interview
For roles with specific requirements, you may need to build your experience. Try working on personal projects to develop your coding skills. You may also try building experience with open source projects and volunteer work. You may also consider taking up small freelance gigs related to C# programming. This will help you both build up your CV and earn some money on the side.
Refine whiteboarding skills
Whiteboarding questions are important and can come up in interviews to test if you have a working knowledge of C#. To work on these, try writing out codes on paper so that you are used to resolving problems by hand. You may also use various online resources available to prepare for whiteboarding exercises for an interview. After you write the code, you should always test it to make sure it is correct.
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