50 C# Interview Questions To Ace Your Next Interview

50 C# Interview Questions To Ace Your Next Interview

Wondering what you need to know when preparing for the C# interview? Read this guide to learn all about C# interview questions and answers.

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As a programming language that debuted in 2000, C# has become one of the leading choices in the programming world. Since C# abstracts away most of the machine-level code, it helps users concentrate more on programming. For these reasons, C# is a good language for beginners.

Even though C# is a multi-paradigm language, it also has some features of functional programming that increase its usefulness and versatility. Therefore, the demand for learning C# is enormous, with many job possibilities. So, to help you ace your C# interview round, here's a list of 50 most-asked C# interview questions.

Master C# fundamentals with the best C# tutorials to create amazing cross-platform Mobile Apps, Games, and PC Programs.

Most comprehensive and up-to-date C# Interview Questions and Answers

This post contains a collection of C# Interview Questions and Answers. This article is written in simple language and is very easy to understand. It is what you need to take a C# interview.

1. What is C#?

Answer: C# is an object-oriented programming language that Microsoft developed in 2000, supported by different operating systems. C# is the primary language that programmers use to create .Net software applications. It allows us to make Windows UI apps, backend services, controls, libraries, Android apps, and even blockchain applications. C# works on the concept of classes and objects just like Java.

2. What are the features of C#?

Answer: The following are some of the features of C#:

  • Open-source
  • Object-oriented
  • Flexible and scalable
  • Easy Parameter Passing
  • C# follows a structured approach.
  • You can compile code on a different platform.

3. Explain what are classes and objects in C#?

Answer: C# is an object-oriented language, and classes are the foundation of it. Generally, a class describes how data is stored and managed within a program. Each class has its properties, methods, and objects that define it.

Objects are real-world entities with specific characteristics, and they are created using class instances. These classes define the types of defined objects. Imagine, for instance, a book-related program. Book is a class with two properties: author and name. Vedas is an object and an example of the class Book in actual programming.

4. Explain how code gets compiled in C#?

Answer: Compilation in C# takes four steps. The steps are as follows:

  • Start by compiling the source code in managed code compatible with the C# compiler.
  • Secondly, combine the newly created code into assemblies.
  • Load the CLR third.
  • Lastly, run the assembly by using CLR to generate output.

5. Describe the different C# classes in detail.

Answer: In C#, we can use four different types of classes:

  1. Static Class: Static classes are non-instantiable classes. We cannot create objects of that class using the new keyword; however, we can call its members by referring to their class name.

  2. Abstract Class: The abstract keyword is used to declare abstract classes. It is not possible to create objects for abstract classes. It must be inherited in a subclass if you intend to use it. Within an Abstract class, you can define abstract or non-abstract methods. There can either be an implementation for the methods inside the abstract class or none; both are equally possible.

  3. Partial Class: This type of class allows their properties, methods, and events to be divided into multiple source files and compiled into a single class.

  4. Sealed Class: A sealed class cannot be inherited from another class, restricting its properties. You can't apply any access modifiers to the sealed class.

6. How can you describe object-oriented concepts in detail?

Answer: C# implements four of the main OOP concepts.

  1. Encapsulation: a technique for enclosing code and data so that any other programs or classes can't alter them. In short, it is a container that prevents other programs from accessing code and data.
  2. Abstraction: Object-oriented programming protects everything, except for the relevant data about any created object, to increase efficiency and security within the program.
  3. Inheritance:Inheritance is the process by which one object uses the properties of another.
  4. Polymorphism: It allows one interface to act as a base class for other classes. Often, this concept is described as a "single interface but multiple actions".

7. Explain different access modifiers in C#?

Answer: These keywords specify the accessibility of class, member, and data type in the program. By using these keywords, other classes can be restricted from performing specific data manipulations.

There are four types of access modifiers- public, private, protected, and internal. There are six different levels of accessibility defined by these modifiers:

  • Public
  • Protected
  • Internal
  • Protected internal
  • Private
  • Private Protected

8. How is C# different from C?

Answer: As we know, C# is an object-oriented language, while C is a procedural language. Among the distinctions is the support for automatic garbage collection in C# by the Common Language Runtime (CLR), while C does not support this feature. C# relies heavily on the .NET framework, while C is a platform-independent language.

9. What is Common Language Runtime (CLR)?

Answer: CLR handles the execution of programs written in various languages, including C#. CLR architecture handles memory management, garbage collection, and security.

10. What is garbage collection in C#?

Answer: Unwanted objects occupy memory, which can be freed up by garbage collection. The heap memory of a class object is allocated automatically when the class object is created. After you have performed all the actions on the object, its memory space becomes wasted. It is vital to free up memory. Garbage collection takes place in three situations:

  • When the occupied memory by the objects exceeds the threshold value,
  • Upon calling the garbage collection method,
  • Low physical memory on your system

11. What is a managed and unmanaged code?

Answer: Using managed code, you can run your code within the .NET framework's managed CLR environment. Runtime environments for managed code run independently of operating systems.

Benefits: Offers a variety of services such as garbage collector and exception handling.

Code that runs outside the .NET framework is unmanaged since it doesn't run on the CLR. Since they do not offer high-level language services, they run without them. C++ is an example of this.

12. What is the difference between an abstract class and an interface?

Answer: Let's explore the differences between abstract classes and interfaces:

  • Abstract classes cannot be instantiated; that is, you cannot use them to create objects. Because all the methods inside an interface are abstract methods, it is like an abstract class.
  • Interestingly, abstract classes can have both abstract and non-abstract methods, but interfaces have only abstract methods.
  • To declare abstract methods, we must use the Abstract keyword since abstract classes can contain abstract and non-abstract methods. The interface, however, does not have such a requirement.

An abstract class includes constructors, while an interface does not.

13. What are extension methods in C#?

Answer: Extension methods allow you to add new methods to existing ones. Methods added to the class are static. When you want to add methods to an existing class but don't have the right to modify it or don't have the perception of the rights, you can create a new static class containing the new methods. Once the extended methods have been declared, bind this class to the existing one, and the new methods will be added to it.

14. What is inheritance? Does C# support multiple inheritances?

Answer: Inheritance is the acquisition of some of the properties of a master class. But, C# does not support multiple inheritances. However, it is possible to use interfaces to inherit the properties using class names in the signature.

C# does not support multiple inheritances because adding multiple inheritances would add unnecessary complexity while providing too little benefit.

15. What are the differences between ref and out keywords?

Answer: The ref keyword in C# passes arguments by reference, not by value. To use the 'ref' keyword, you need to mention 'ref' explicitly.

void Method(ref int refArgument)
{
   refArgument = refArgument + 10;
}
int number = 1;
Method(ref number);
Console.WriteLine(number);
// Output: 11

The out keyword in C# passes arguments within methods and functions. An argument is passed in a method as a reference to return multiple values using the 'out' keyword. Although it is the same as the ref keyword, the ref keyword must be initialized before passing.

The out and ref keywords are helpful when we want to return values within the same variables passed as arguments.

public static string GetNextFeature(ref int id)  
{  
   string returnText = "Next-" + id.ToString();  
   id += 1;  
   return returnText;  
}  
public static string GetNextFeature(out int id)  
{  
   id = 1;  
   string returnText = "Next-" + id.ToString();  
   return returnText;  
}

16. What is break and continue statements in C#, explain?

Answer:

BreakContinue
Break statements can be used in both switch and loop (for, while, and do-while ) statements.Continue statements can only be used in the loop (for, while, do) statements.
When a break statement is executed, the switch or loop statement terminates abruptly.If you use a continue statement to end a loop, it continues to the next iteration level without performing a subsequent step.
Once the compiler encounters a break statement and comes out of the inner loop, the loop or switch leaves the inner loop immediately.The next loop iteration is caused by a continue placed inside a nested loop within a switch.

17. What is the difference between an Array and ArrayList in C#?

Answer: Arrays are collections of similar variables grouped under one name, as opposed to an ArrayList, a collection of objects that can be indexed individually. ArrayList offers several features like dynamic memory allocation, adding, searching, and sorting items in the ArrayList.

  • When declaring an array, the size of the items remains constant. Therefore, memory allocation is not flexible. With ArrayList, however, it can be dynamically increased or decreased.
  • ArrayList belongs to the system.collection namespace, while Array belongs to the system.array namespace.
  • In contrast, every item is the same data type in an array, whereas it can be a different data type in an array list.
  • In contrast to arrays, ArrayLists can accept null values.

18. What is Boxing and Unboxing in C#?

Answer: The following two functions are used to typecast data types:

  • Boxing: It converts value type (int, char, etc.) to reference type (object), an implicit conversion process using object value. Example:
int num = 23; // 23 will assigned to num
Object Obj = num; // Boxing
  • Unboxing: Unboxing converts reference types (objects) to value types (int, char, etc.) using exact conversion. Example:
int num = 23;         // value type is int and assigned value 23
Object Obj = num;    // Boxing
int i = (int)Obj;    // Unboxing

19. What are partial classes in C#?

Answer: Classes that implement the functionality of a single class in multiple files are called partial classes. During compilation, multiple files are combined into one. You can use the partial keyword to create a partial class.

It is easy to split the functionalities of methods, interfaces, and structures into multiple files. Additionally, you can nest partial classes.

20. What are Properties in C#?

Answer: In C#, properties are public members of a class through which they can access private members. By encapsulating some sensitive properties, you can conceal them from users by making the variables private. In a class, private members are not accessible. As a result, in C#, properties allow you to access and modify private members easily.

Accessors, also known as get and set methods, can be used to assign values. The get method extracts the value, while the set method assigns it to the variables.

21. What is the difference between late binding and early binding in C#?

Answer: One of the principal concepts of OOPS is Polymorphism, which includes late binding and early binding.

In C#, the .NET framework performs the binding when an object is assigned to an object variable.

It is called early binding when binding takes place at compile time. Static objects are investigated, and their properties examined. Early binding reduces run-time errors considerably and makes the code execute quickly.

However, late binding occurs when binding occurs during run-time. Late binding occurs when objects are dynamic (based on the data they contain) at run time. During run-time, it is slower because it looks through.

22. What are Indexers in C#?

Answer: Indexers are named smart arrays because they allow access to a member variable. By using indexers, member variables can benefit from array features. Indexers are not static members. They are created using the Indexer keyword.

23. What are the different ways in which a method can be overloaded in C#?

Answer: Overloading occurs when a method has the same name but carries different values to operate in a different context. It is impossible to override any method other than main().

To overload methods in C#:

  • Change the number of parameters in a method, or
  • Change the order of parameters in a method, or
  • For parameters, use different data types.
  • In this way, you can overload a method multiple times.

Example:

public class Area {
   public double area(double x) {
       double area = x * x;
       return area;
   }
   public double area(double a, double b) {
       double area = a * b;
       return area;
   }
}

24. What is Reflection in C#?

Answer: Metadata is extracted from C# datatypes during runtime by Reflection.

In the .NET framework, you can add Reflection by using the System.Reflection namespace to retrieve the type, which can be anything from:

  • Assembly
  • Module
  • FieldInfo
  • EventInfo
  • PropertyInfo
  • Enum
  • MethodInfo
  • ConstructorInfo
  • MemberInfo
  • ParameterInfo
  • Type

25. What is the difference between constant and read-only in C#?

Answer: A const keyword in C# allows you to declare a constant field throughout the program. As a result, once a variable has been declared const, you cannot change its value throughout the program.

Note: A constant in C# can be a number, string, null reference, or boolean value.

In contrast, a read-only keyword allows you to assign a variable only when it is declared or in a constructor of the same class in which it is declared.

By default, constants are static, whereas read-only objects should have an initial value as soon as the constructor is declared. Constants can be declared within functions, while you can use read-only modifiers with reference types.

26. Difference between the Equality Operator (==) and Equals() Method in C#?

Answer: Despite both being used to compare two objects by value, they are used differently. For instance:

int x = 10;
int y = 10;
Console.WriteLine( x == y);
Console.WriteLine(x.Equals(y));
Output:
True
True

Equality operator (==) is a reference type, meaning it will return true if both references point to the same object if the equality operator is used.

Equals() method: This method compares the values carried by objects. int x=10, int y=10. By comparing x==y, we compare every value brought by both x and y, and they are equal, so the comparison returns true.

Equality operator: Compares by reference.

Equals(): Compares by value.

27. What are the Arrays in C#?

Answer: Arrays are groups of similar elements grouped under one name.

As an example, we have various tea Atea[4]: [green tea, chamomile tea, black tea, lemon tea]. There are a fixed number of elements in the array, determined by their length. In C#, memory is allocated dynamically for array elements. In this method, values are stored in an array sequentially.

Here are a few pointers for arrays in C#:

  • The memory allocation is dynamic.
  • C# treats arrays as objects.
  • By detecting the number of elements in the array, we can find the length of the array.
  • Members of the array are ordered with the index value 0 at the beginning.
  • Reference types are derived from base array types.

28. Explain the use of 'using' statements in C#.

Answer: Using statements are used to control the use of one or more resources within the program. Resource consumption and release are continuous. This statement is responsible for managing unused resources and releasing them automatically.

Using statements work well when you create an object which uses a resource and when the object is finished using the resource, you make sure to call its dispose method to release the resource.

29. Explain in detail the finalize method in C#?

Answer: The finalize () method is defined in the object class that is used for cleanup activities. The garbage collector generally calls this method whenever an object's reference hasn't been used for a long time.

When you use garbage collection to manage resources, it automatically frees them. But if you want to free unused resources, such as file handles, data connections, etc., you must implement the finalize method manually.

30. Describe the C# dispose of the method in detail.

Answer: The disposeof() method releases the unused resources by an object of the class. (unused resources like files, data connections, etc.) This method is declared in the interface called IDisposable, which the class implements by defining the interface IDisposable body. A programmer must implement the dispose method manually for efficient use of resources; it is not called automatically.

31. How you can define the exception handling in C#?

Answer: A problem that occurs during program execution is an exception. In cases where exceptions are raised, handling exceptions offer a simple method of passing control to another program. C# exceptions are handled using four keywords: try, catch, finally, throw.

  • Try: A raised exception finds a particular block of code to get handled. You can use as many catch blocks as you wish to handle different types of exceptions raised in your program.
  • Catch: Within this catch block, you can handle a raised exception. You can specify what steps you want to take to fix the error or ignore it by suppressing it with code.
  • Finally: If you still want some instructions to be displayed despite an error, you can use those statements within the finally block, and the screen will display the instructions.
  • Throw: The throw statement allows you to throw an exception. You can see the type of error you are getting there.

32. What are the control statements that are used in C#?

Answer: You can use control statements to control the progression of your set of instructions, and we mostly use if statements. These are a few types of if statements that we may use in a program to control execution flow.

The four types of if statements are:

  • If: In an, if statement, the user specifies a condition to satisfy their programming condition. The set of instructions will be executed if it returns true.

  • If-else: The if-else statement checks for the given condition. The flow will transfer to the else statement if the condition turns out to be false, and the else it will execute instructions. The if instructions will be executed if the condition is true.

  • Nested If: The nested if statement checks for the condition. If the condition is true, it will check the inner if statement and keep going until the last if statement is reached. It will execute the particular if instructions based on the condition and stop the loop if any conditions are met.

  • If-else-if: When else-if checks for the given condition, if it is not true, the control will move to the next else condition. It will keep checking for next else conditions if that condition is not true. Whenever a condition is not met, the last else instruction gets executed.

33. How can you check if a number is an Armstrong number or not with C#?

Answer:

using System;  
  public class ArmstrongDemo  
   {  
     public static void Main(string[] args)  
      {  
       int  n,b,sum=0,num;      
       Console.Write("Enter the Number= ");      
       n= int.Parse(Console.ReadLine());     
       num=n;      
       while(n>0)      
       {      
        b=n%10;      
        sum=sum+(b*b*b);      
        n=n/10;      
       }      
       if(num==sum)      
        Console.Write("Armstrong Number.");      
       else      
        Console.Write("Not Armstrong Number.");      
      }  
  }

Output:

Enter the Number= 371

Armstrong Number.

34. What are various types of comments in C#, explain with example?

Answer: There are three types of comments in C#:

Single line comment

Syntax: //single line

Multiple line comment

Syntax: /* multiple lines

*/

XML comment

Syntax: /// set error

35. What are the constructors?

Answer: When creating an object in C#, a special method is automatically invoked. Usually, it initializes the data members of a new object, and the name of the procedure is the same as the class or structure name. Two types of constructors exist:

  • Default constructor: There is no parameter to pass.
  • Parameterized constructor: a constructor invoked with parameters passed to the class when the object is created.

36. C# program to remove an element from the queue.

Answer:

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Application
{
 class DemoProgram
 {
  static void Main(string[] args)
  {
   Queue qs = new Queue();
   qs.Enqueue(1);
   qs.Enqueue(2);
   qs.Enqueue(3);
   foreach (Object ob in qs)
   {
    Console.WriteLine(ob);
   }
    Console.WriteLine(); Console.WriteLine();
    Console.WriteLine("Total number of elements in the Queue " + qs.Count);
    Console.WriteLine("Does the Queue contain " + qs.Contains(3));
    Console.ReadKey();
   }
 }
}

37. Compare Virtual methods and Abstract methods.

Answer: The default implementation of a Virtual method must exist, and in a derived class, it can be overridden by using the override keyword. Abstract methods, on the other hand, have no implementation and are inherited from their abstract class. Implementation of the abstract method is a requirement for the derived class. We can use an override keyword here, even though it is not necessary.

38. How to find if a number is a palindrome or not in C#.

Answer:

using System;  
  public class PalindromeNum  
   {  
     public static void Main(string[] args)  
      {  
          int n,r,num=0,Dem;    
          Console.Write("Enter the Number: ");   
          n = int.Parse(Console.ReadLine());  
          dem=n;      
          while(n>0)      
          {      
           r=n%10;      
           num=(num*10)+r;      
           n=n/10;      
          }      
          if(dem==num)      
           Console.Write("Number is Palindrome.");      
          else      
           Console.Write("Number is not Palindrome");     
    }  
  }

39. What are Namespaces in C#?

Answer: Namespaces are used to organize large code projects. In C#, the system namespace is the most commonly used. Using the namespace keyword, one can create namespaces. It is possible to use one namespace inside another, called Nested Namespaces.

40. What are I/O classes in C#? Define some of the most commonly used ones.

Answer: In C#, the System.IO namespace contains several classes that perform file operations, such as creation, deletion, closing, and opening. C#'s most commonly used I/O classes include:

  • File – Manipulates a file
  • Path – Performs operations on some path information.
  • StreamReader – Reads characters from a stream
  • StreamWriter – Writes characters to a stream
  • StringReader – Reads a string buffer
  • StringWriter – Writes a string buffer

41. Give a detailed explanation of Delegates in C#

Answer: Delegates are variables that contain references to methods. It is a function pointer or reference type. Delegates and methods that they refer to can both have the same signature. System.Delegate is the namespace from which all delegates derive.

The following example shows how to declare a delegate:

public delegate AddNumbers(int n);

Once the delegate has been declared, an object must be created with the new keyword, such as:

AddNumbers an1 = new AddNumbers(number);

The Delegate provides a kind of encapsulation for the reference method, which gets internally called with the call to the delegate. As an example, we have a delegate myDel that takes an integer value as a parameter: public delegate int myDel(int number); public class Program { public int AddNumbers(int a) { Int Sum = a + 10; return Sum; } public void Start() { myDel DelgateExample = AddNumbers; } }

42. Name some of the most common places to look for a Deadlock in C#.

Answer: To identify deadlocks, one should look for threads that become stuck on any of these:

  • WaitOne() methods (When working with AutoResetEvent/EventWaitHandle/Mutex/Semaphore)
  • lock statements (In all cases)
  • .Result, .GetAwaiter().GetResult(), WaitAll(), and WaitAny() (When working with Tasks)
  • Join() (When working with Threads)
  • Dispatcher.Invoke() (When working in WPF)

43. Give a brief explanation of Thread Pooling in C#.

Answer: In C#, a Thread Pool is a collection of threads. These threads perform tasks without interfering with the main thread's execution. Threads in thread pools return to the pool after they have completed execution. The namespace System.Threading.ThreadPool contains classes that manage threads in a thread pool and their operations.

44. What do you mean by Constructor Chaining in C#?

Answer: In C#, constructor chaining is the process of connecting two or more classes in a relationship as an inheritance. In constructor chaining, the base keyword maps every child class constructor to the parent class constructor implicitly.

Note: When serializing C# code, classes are converted to XSD-compliant code using the Xsd.exe tool.

45. What can you tell us about the XSD file in C#?

Answer: In asynchronous programming, processes can run in isolation from other processes. For C#, use the Async and Await keywords to create asynchronous methods.

46. What is the Race condition in C#?

Answer: The race condition occurs when two threads access the same resource simultaneously and try to change it. It is almost impossible to predict which thread will be able to access the resource first. Whenever two threads attempt to write to the same resource, the last value written is saved.

47. What do you understand by Get and Set Accessor properties?

Answer: In C#, Get and Set are accessors made using properties. The value of a private field can be read and written via a property. Such private fields are accessed using accessors. Meanwhile, the Get property is used to return the value of a property, while Set is used to set it.

48. What is Singleton Design Patterns in C#? Give an example of their implementation.

Answer: In C#, a singleton is a class that can create only a single instance of itself and provides access to that single instance. Typically, singletons don't allow parameters to be specified, because the second request of the same instance with a variable can cause problems. In C#, the following example illustrates Singleton Design Patterns:

namespace Singleton {
class Program {
static void Main(string[] args) {
Calculate.Instance.ValueOne = 10.5;
Calculate.Instance.ValueTwo = 5.5;
Console.WriteLine("Addition : " + Calculate.Instance.Addition());
Console.WriteLine("Subtraction : " + Calculate.Instance.Subtraction());
Console.WriteLine("Multiplication : " + Calculate.Instance.Multiplication());
Console.WriteLine("Division : " + Calculate.Instance.Division());
Console.WriteLine("\n----------------------\n");
Calculate.Instance.ValueTwo = 10.5;
Console.WriteLine("Addition : " + Calculate.Instance.Addition());
Console.WriteLine("Subtraction : " + Calculate.Instance.Subtraction());
Console.WriteLine("Multiplication : " + Calculate.Instance.Multiplication());
Console.WriteLine("Division : " + Calculate.Instance.Division());
Console.ReadLine();
}
}
public sealed class Calculate {
private Calculate() {}
private static Calculate instance = null;
public static Calculate Instance {
get {
if (instance == null) {
instance = new Calculate();
}
return instance;
}
}
public double ValueOne {
get;
set;
}
public double ValueTwo {
get;
set;
}
public double Addition() {
return ValueOne + ValueTwo;
}
public double Subtraction() {
return ValueOne - ValueTwo;
}
public double Multiplication() {
return ValueOne * ValueTwo;
}
public double Division() {
return ValueOne / ValueTwo;
}
}
}

Whenever a class contains only one instance, it is referred to as a Singleton Design Pattern, which facilitates global access to the class. There are multiple ways of implementing Singleton Design Patterns in C#.

49. Explain the different states of a Thread in C#?

Answer: In C#, threads can have the following states:

  • Aborted – The thread is dead but it is not stopped
  • Stopped – The thread has stopped executing.
  • Running – The thread is executing
  • Suspended – The thread has been suspended
  • Unstarted – The thread is created but not yet running.
  • WaitSleepJoin – A thread calls sleep, waits for another object, and then calls join on another thread

50. What do you understand by regular expressions in C#? Write a program that searches a string using regular expressions.?

Answer: In regular expressions, a set of inputs is matched by a template. It can include constructs, character literals, and operators. Regex is used to parse and replace characters in strings. The following code uses Regex to search for a string "C#" against the set of inputs from the languages array:

static void Main(strong[] args)
{
string[] languages = {“C#”, “Python”, “Java”};
foreach(string s in languages)
{
if(System.Text.RegularExpressions.Regex.IsMatch(s,“C#”))
{
Console.WriteLine(“Match found”);
}
}
}

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