C# Interview Questions and Answers 2021

C# is a straightforward, modern and broadly useful Object-based programming language created by Microsoft inside its .NET framework. In a world of high competition, everybody wishes to be 2 steps ahead gaining as much experience as possible. To aid with that, here are some C# interview questions and answers so that you can stay ahead of the game. Thank us later!

Beginner C# Interview Questions for Freshers:

1. Define C#:

• C# is one of the most useful Object-Oriented Programming (OOP) language. It is also type-safe in nature. C# allows coders to create a wide variety of programs and applications within the .NET Framework.

2. What are some of the tasks that C# can accomplish?

• C# opens doors to newer avenues for its programmers. They can create Windows-based client applications, apps based on databases and client-servers, XML web services and manage distributed components.

3. What do you mean by CLR?

• CLR refers to the execution engine of .NET Framework wherein all the applications that come under .NET are systematically run under the supervision of CLR. All the applications that function under CLR are portable, secure and support automatic memory management. 

4. What does CLR contain internally?

• CLR mainly consists of a JIT compiler, an efficient Security Manager as well as a garbage collector. 

5. Define an object:

• An object can be defined as an instance of a class in C# which we can use as a portal to access the different methods of that class. The keyword ‘new’ is used to create new objects in a class. Any class that creates an object within the system’s memory will indefinitely contain all the information of the methods, behavior, and variables associated with that class. An object typically exists in real-time, for instance, it can be a phone, a TV, a book, etc.

6. Differentiate between out and ref parameters:

• The main difference between out and ref parameters is that before an argument is passed to a method as a ref, it has to be initialized. On the other hand, any argument that is passed to the method as out does not have to be initialized.

7. What are jagged arrays?

• Jagged arrays are one of the most important components of C#. A jagged array typically contains elements that are also of an ‘array’ type. These elements can vary in size and dimensions. Simply put, an array of arrays is called a jagged array. Within your program it will look like the following:

int[] JaggedArray = new in[5][];
 
    JaggedArray[0]=new int[3];
    JaggedArray[1]=new int[9];
    JaggedArray[2]=new int[11];
 
    JaggedArray[0]=new int[]{8,6,7};

8. Differentiate between boxing and unboxing:

• Boxing can be defined as the process of conversion in which a value type is converted into a reference type. For example,

int a=9;
    Object obj=a;
    // done via boxing

• Contrary to boxing, unboxing refers to the opposite. It is the process by which a reference type is converted into a value type. As you can see in the below example:

int b=Convert.ToInt32(obj);
    //done via unboxing

9. Differentiate between constants and read-only:

• Constant variables are the type of variables that are initialized and declared during compile time itself. The coder cannot change the value of this variable later. 
• Read-only is only utilized when the developer wants to assign the value to a variable during run time.

10. What are Static Classes?

• There is no substantial difference between a static class and a non-static class, apart from the fact that there are no instance variables or objects within a static class. Since there are no objects within that class, you can only access the elements of that static class by using the name of that class.

11. What do you understand by ‘sealed’ classes?

• When we want to restrict any class to be inherited, we often seal that particular class. We cannot specify any sealed class as the base class for our program as it will lead to an exception. Developers assign a sealed modifier to the class that they want to seal in order to restrict derivation from that class. That syntax if a sealed class is as follows:

sealed class <abc>

12. Define delegates:

• Delegates work similarly to function pointers. Delegates are different from function pointers because unlike function pointers, they are type-safe in nature.
• Coders use delegates extensively as they allow the coder to write many more generic functions which are also type-safe.

13. What are the advantages of using delegates?

• Delegates allow the coder to write many more generic type-safe functions that a function pointer would not allow.
• Delegates are also used to asynchronously call a method.
• It is known to effectively improve the application’s performance.
• It helps to encapsulate the caller from the method’s call.

14. Differentiate between abstract class and interface:

• All the methods that are within an interface have no definition; they are only declared as methods.
• As opposed to interfaces, abstract classes have methods that are declared as well as defined, thus, concrete in nature.
• All the methods within an interface class are public.
• The methods within an abstract class may be public or even private.

15. Explain the differences between method overloading and method overriding:

• In method overriding, in order to change the behavior of any method, we typically change the definition of that method. While overloading a method, you essentially create a method in the same class that has the same name but which has varied signatures.

16. Define dynamic variables in C#:

• A dynamic variable functions exactly as its name suggests. It can easily store values of any data type, which does not usually happen with non-dynamic variables. The values are checked for these variables during run-time itself.

17. Explain the difference between a class and a struct:

• Classes are typically variables that are of reference-type, whereas, structs are variables of value-type.
• Since structs are stored on stacks, it tends to result in quicker retrieval but it may cause more overhead.
• Structs restrict inheritance.
• The ‘class’ keyword is used to define classes whereas, the ‘struct’ keyword is used to define structs.

18. Name the access modifiers in C#:

• The different access modifiers available within C# are internal, protected internal, protected private, and public.

19. Define constructors:

• A constructor can be defined as a special method of a class that is automatically invoked when an object of the class is created.
• While creating an instance, or an object of a class, constructors are typically used to initialize private fields.
• If a constructor is not manually created, the compiler will then automatically create a constructor in the class in which all numerical fields are initialized to zero, as well as, all object fields and strings are initialized to null.
• The syntax for constructors is as follows:

[Access Modifier] ABC([parameters])

20. Name the different types of constructors:

The different types of constructors are as follows:

• Static Constructor
• Private Constructor 
• Copy Constructor
• Default Constructor
• Parameterized Constructor

21. Explain Polymorphism:

• Polymorphism can be defined as changing the format of any object. When an object can be morphed, or transformed into multiple formats, that is when polymorphism takes place. Polymorphism can take place in one of two ways: method overriding and method overloading.

Advanced C# Interview Questions for Experienced Professionals:

1. Explain the differences between Dictionary and Hashtable:

• A dictionary is not thread-safe, whereas, a hashtable is thread-safe in nature.
• Values stored in dictionaries need not be boxed or unboxed. To the contrary, the values in a hashtable need to be boxed and unboxed as they are stored as objects.
• When the coder attempts to access a key or variable that does not exist in a dictionary, C# throws an exception that says, “KeyNotFoundException” whereas, a hashtable simply returns a null value.

2. Define a string and string builder:

• A string cannot be modified and always creates new instances of string types in the system’s memory. A string is a data type that contains a collection of elements. For instance, 

string abc="this is a string";
 //instead of changing the existing string, you can create a new one or add to it 
 abc +=" and this is the addition";
 Console.WriteLine (abc);

OUTPUT:

this is a string and this is the addition

• A string builder is contrary to a string, in the sense that it allows changes to be made to the string builder, instead of creating newer instances every time. The changes will be made to the string builder within one memory slot.

StringBuilder xyz= new StringBuilder("");
xyz.Append("String Builder");

3. Explain the differences between Dispose() and Finalize() methods:

• The Dispose() method is called when the coder wishes for any object to release unmanaged resources.
• On the contrary, Finalize() methods are typically called to perform the same function but, unlike Dispose(), it does not assure an object’s garbage collection.

4. Define the function of a protected internal member variable within a C# class:

• The special feature of a protected internal access modifier is that it hides and restricts access to its member functions and member variables from other functions and objects. This restriction does not apply to child classes inside the same application. Protected Internal access modifiers are also extensively used while implementing inheritance.

5. Define the function of a Null Coalescing Operator in C#:

• The null Coalescing Operator is typically used with nullable reference types, as well as, value types that are nullable in nature. When a developer wishes to convert an operand to a value type operand that is also nullable, they make use of Nullable Coalescing Operator.

6. Why C# over other programming languages?

• In today’s day and age, C# is by far the most preferred programming language used to make games, websites, software, and so much more. Since it is deeply rooted in Microsoft’s mechanisms, it is safe to say that they will work hard and fast to keep C# updated as technology rapidly evolves alongside it. With so many game developers, website designers, and software programmers opting for C# over other scripts, it is easy to see why everyone should to. C# offers an unmatched level of versatility and scope to improve which is hard to come by elsewhere.

7. What are the different types of data used in C#?

The different types of data used in C# are as follows:

• Int – Contains a whole number within 4 bytes
• Long – Contains a whole number within 8 bytes 
• Bool – Contains true/ false type of value
• Float – Contains fractional numbers within 4 bytes
• Double – Contains fractional numbers within 8 bytes
• Char – Contains a single number or character
• String – Contains a chain or sequence of characters

8. In C#, define an array.

• In C#, an array represents a collection of values for a given variable instead of having to allocate separate variables for different values. An array can be used by utilizing the square brackets [ ]. An array is versatile and lucrative in terms of how it can be accessed, stored, modified, and manipulated.

9. What is an ‘enum’?

• In C#, an ‘enum’ refers to a special class that involves unchangeable variables. Enums are categorized as ‘constants’, even if they are variables. Generally, developers and coders use these enums with switch statements in order to check the effects of one variable on the following statements and their imminent results. The value of an enum must be assigned and modified by the programmer themselves, thus, remaining constant otherwise. This constant variable then affects the following variables. The default value for the first enum character is 0 and then 1 and so on.

10. In C#, what is an exception?

• In coding and programming, much like any other discipline, people tend to make mistakes. Programming is not particularly known to be forgiving, that is why the slightest mistake in the code can result in unexpected conclusions. When programmers make an error in their code, the C# operation spontaneously generates an error message. The generation of an error message is called ‘throwing an exception’ in C#. What one must note is that exceptions in C# can also be manipulated and used for various purposes by the coder or programmer. ArithmeticException, FileNotFoundException, IndexOutOfRangeException, TimeOutException, etc are just some of the exception classes available for programmers to use in C#

11. How does one avoid being thrown an exception?

• There are multiple ways to avoid error messages (exceptions) in C#. The first and most obvious method would be to carefully read and re-read your code as and when you go through with it. It may seem mundane but it is one of the most important things a programmer must do to ensure coherent code. The second method is by using the ‘Try…Catch’ keywords. These keywords come in a pair and can be used to weed out errors in your code. One can type the ‘Try’ statement followed by the piece of code to be judged and then follow it with the ‘catch’ statement, commanding the program to examine that piece of code for any exceptions. C# will then automatically weed out the exceptions following the ‘try…catch’ pair of statements.

12. What are the benefits of using Generics in C#?

• For a beginner or someone who is not well-versed with the programming language, using Generics will definitely come in handy. They are better than non-generic commands because a) they are safe. This means that Generics are type-safe, which makes them forgiving and less likely to result in errors since non-generics are not type-safe and b) they are efficient. They are the fill-in-the-blanks cheat sheet for anyone who does not know enough about the different nuances within this programming language.

13. Do you know what C# was originally set out to be called?

• C# was initially named as COOL (C-like Object-Oriented Language) in an attempt to make it sound, well, cooler than other programming languages that were being used in the market. Microsoft could not sustain this particular nomenclature for the unavailability of trademark licensing.

14. Name some of the applications or software that have been written using C#.

• Windows Installer XML
• Microsoft Visual Studio
• Paint.NET
• Open Dental
• KeePass
• FlashDevelop
• Banshee
• NMath
• Pinta
• OpenRA

15. Define ‘Class Members’.

• Class members typically consist of Fields and Methods, Fields can be described as variables within a class. These variables can be accessed and modified by using the dot (.) syntax and converting that class into an object. A method is used to describe the way in which a class behaves. It represents the class’s functions and actions. Collectively, fields and methods are termed as ‘class members.’

16. Why do programmers use the ‘while loop’?

• In C# a loop is used to run a specific set of commands and methods in a continuous sequence for a pre-determined limit of time set by the programmer themselves. A ‘while loop’ is a form of looping where the set of commands that follow the while loop are only repeated if the value of the condition mentioned is true. For instance, a command will only be looped if a condition is positively fulfilled by the response. Programmers tend to use while loops to minimize errors, maximize efficiency, and save time. It helps them assess feedback quicker and make programming work for them.

17. How do you lock a class and why should you do it?

• Many programmers choose to lock specific classes by using the ‘sealed’ keyword to maximize security and prevent unwanted activity. A security command or method, if left unlocked can give way to any programmer creating a backdoor to that security system. In this case, locking that class will allow the developer or original programmer to ensure that the data within that class cannot be accessed, modified, or moved without their knowledge and consent.

18. How is C# different from C++?

• C++ is a lower-end programming script that adds object-oriented features to its base language C whereas C# is a higher-end programming language. C++ compiles down to machine code whereas C# ‘compiles’ down to CLR (Common Language Runtime), which is interpreted by JIT in ASP.NET.

19. In C#, what do you mean by type-casting?

• Type-casting in C# refers to the assignment of value from one data type to another. There are two types of type-casting used in C#, implicit and explicit to be precise. Implicit type-casting represents the change of data value from a smaller data type to a bigger data type (char<int<long<float<double) Implicit type-casting happens automatically, whereas explicit type-casting means the change of data value from a bigger to a smaller data type (double>float>long>int>char) This change needs to occur manually.

20. List down the different IDE’s Provided by Microsoft for C# Development.

Following are a few IDE’s for C# development:

• MonoDevelop
• Visual Studio Express (VCE)
• Visual Studio (VS)
• browxy
• Visual Web Developer

21. What are some of the limitations of using C#?

• Since C# is a part of the .NET framework, the server running the application has to be Windows. Simply put, any .NET application needs a Windows platform to operate. Many new companies work with Linux servers since it’s a cheaper environment in comparison. You need Windows hosts to run a .NET application. Additionally, the GUI (Graphic User Interface) is also said to be poorer than its competitors.

Staying ahead of the game can be hard, but with this guide, it should be easier, These C# Interview Questions will set you up adequately so that you know what you are up against and know more than you thought you did. Since this article provides questions and answers for beginners and experienced professionals alike, it will give you a good idea of your current level of expertise and help you learn quicker. Interviews can be stressful, especially ones pertaining to technical knowledge and jargon such as C#, but this guide will be your blueprint to acing your C# Interview. Good luck!