August 28, 2024
Are you preparing for your first C# interview and wondering what questions you might face?
Understanding the key C# interview questions for freshers can give you more clarity.
With this guide, you’ll be well-prepared to tackle these C# interview questions and answers for freshers and make a strong impression in your interview.
Practice C# Interview Questions and Answers
Below are the top 50 C# interview questions for freshers with answers:
1. How do you declare and initialize a variable in C#?
Answer:
Declare a variable by specifying its type and name, followed by initialization with a value using the assignment operator.
int number = 5;
2. What is the difference between == and Equals() in C#?
Answer:
== compares the reference or value type of objects, while Equals() compares the actual content of the objects.
string a = “hello”;
string b = “hello”;
bool result = a == b; // True
bool result2 = a.Equals(b); // True
3. How do you create a constant in C#?
Answer:
Use the const keyword to declare a constant, which means its value cannot be changed after initialization.
const double Pi = 3.14159;
4. What is the purpose of the using statement in C#?
Answer:
The using statement is used to include namespaces and ensure that resources are disposed of correctly at the end of their usage.
using System.IO;
5. How do you define an enum in C#?
Answer:
Define an enum using the enum keyword, followed by the enum name and a list of named constants.
enum Days { Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday }
6. How do you create a class in C# and instantiate an object of that class?
Answer:
Define a class using the class keyword and instantiate it using the new keyword.
class Car {
public string Make { get; set; }
}
Car myCar = new Car();
7. What is the difference between a class and an object in C#?
Answer:
A class is a blueprint or template for objects, while an object is an instance of a class, containing data and methods defined in the class.
Car myCar = new Car(); // `myCar` is an object, `Car` is the class
8. How do you implement encapsulation in C#?
Answer:
Encapsulation is implemented using access modifiers like private, protected, and public to restrict access to class members.
class Account {
private decimal balance;
public void Deposit(decimal amount) {
balance += amount;
}
}
9. What is inheritance, and how do you implement it in C#?
Answer:
Inheritance allows a class to inherit members from another class using the : symbol. The derived class inherits properties and methods from the base class.
class Vehicle {
public string Brand { get; set; }
}
class Car : Vehicle {
public int Wheels { get; set; }
}
10. What is polymorphism in C#, and how do you achieve it?
Answer:
Polymorphism allows methods to have different implementations in derived classes. It is achieved using method overriding with the virtual and override keywords.
class Animal {
public virtual void Speak() {
Console.WriteLine(“Animal speaks”);
}
}
class Dog : Animal {
public override void Speak() {
Console.WriteLine(“Dog barks”);
}
}
11. How do you implement an interface in C#?
Answer:
An interface is implemented by a class using the : symbol. The class must provide implementations for all interface members.
interface IDriveable {
void Drive();
}
class Car : IDriveable {
public void Drive() {
Console.WriteLine(“Driving a car”);
}
}
12. What is the difference between an abstract class and an interface in C#?
Answer:
An abstract class can have method implementations and fields, while an interface can only have method declarations. A class can inherit multiple interfaces but only one abstract class.
abstract class Animal {
public abstract void MakeSound();
}
interface IRun {
void Run();
}
13. How do you handle exceptions in C#?
Answer:
Use try, catch, and finally blocks to handle exceptions, allowing you to manage runtime errors gracefully.
try {
int result = 10 / 0;
} catch (DivideByZeroException ex) {
Console.WriteLine(“Cannot divide by zero”);
} finally {
Console.WriteLine(“End of try-catch block”);
}
14. What is a delegate in C#, and how do you declare and use it?
Answer:
A delegate is a type-safe function pointer. It is declared using the delegate keyword and can point to methods with a matching signature.
public delegate void PrintMessage(string message);
PrintMessage pm = new PrintMessage(Console.WriteLine);
pm(“Hello, Delegates!”);
15. How do you implement a generic class in C#?
Answer:
A generic class is defined using a type parameter that allows the class to operate on different data types.
class GenericClass<T> {
public T Field;
public GenericClass(T value) {
Field = value;
}
}
GenericClass<int> myClass = new GenericClass<int>(10);
16. How do you use LINQ to filter and sort a list of integers?
Answer:
LINQ allows you to query collections using query syntax or method syntax, enabling powerful filtering, sorting, and aggregation operations.
int[] numbers = { 5, 3, 9, 1 };
var sortedNumbers = from n in numbers
where n > 2
orderby n
select n;
17. What is the purpose of the List<T> class, and how do you add elements to it?
Answer:
List<T> is a generic collection that provides dynamic array-like storage for elements. Use the Add method to add elements.
List<int> numbers = new List<int>();
numbers.Add(1);
numbers.Add(2);
18. How do you find the maximum value in a list using LINQ?
Answer:
Use the Max() method provided by LINQ to find the maximum value in a list or collection.
List<int> numbers = new List<int> { 1, 5, 3 };
int maxValue = numbers.Max();
19. What is the difference between IEnumerable and IQueryable in C#?
Answer:
IEnumerable is used for in-memory collections, while IQueryable is designed for querying data from out-of-memory sources like databases, allowing for deferred execution and remote querying.
IEnumerable<int> numbers = new List<int> { 1, 2, 3 };
20. How do you group data using LINQ in C#?
Answer:
Use the group by clause in LINQ to group elements in a collection based on a specific key.
var grouped = from n in numbers
group n by n % 2 into g
select g;
21. How do you read the contents of a file line by line in C#?
Answer:
Use the StreamReader class in a using block to read the contents of a file line by line.
using (StreamReader sr = new StreamReader(“file.txt”)) {
string line;
while ((line = sr.ReadLine()) != null) {
Console.WriteLine(line);
}
}
22. What is the method to write text to a file in C#?
Answer:
Use the StreamWriter class to write text to a file, which creates a new file or appends to an existing one.
using (StreamWriter sw = new StreamWriter(“file.txt”)) {
sw.WriteLine(“Hello, World!”);
}
23. How do you check if a file exists in C#?
Answer:
Use the File.Exists() method to check whether a specific file exists in the specified path.
bool exists = File.Exists(“file.txt”);
24. What is the method to copy a file from one location to another in C#?
Answer:
Use the File.Copy() method to copy a file from one directory to another, specifying the source and destination paths.
File.Copy(“source.txt”, “destination.txt”);
25. How do you delete a file in C#?
Answer:
Use the File.Delete() method to delete a file from the filesystem by providing its path.
File.Delete(“file.txt”);
26. What is an event in C#, and how do you declare one?
Answer:
An event is a message that objects send to signal the occurrence of an action. Declare an event using the event keyword and a delegate type.
public event EventHandler MyEvent;
27. How do you subscribe to an event in C#?
Answer:
Subscribe to an event by attaching an event handler method using the += operator.
MyEvent += new EventHandler(EventHandlerMethod);
28. What is a multicast delegate in C#?
Answer:
A multicast delegate can reference multiple methods. When invoked, all methods in the delegate chain are called in sequence.
public delegate void Notify();
Notify del = Method1;
del += Method2;
29. How do you remove a method from a delegate’s invocation list in C#?
Answer:
Use the -= operator to remove a method from a delegate’s invocation list.
del -= Method1;
30. How do you raise an event in C#?
Answer:
Raise an event by invoking it, typically using a protected virtual method to ensure it’s properly raised by derived classes.
protected virtual void OnMyEvent() {
MyEvent?.Invoke(this, EventArgs.Empty);
}
31. How do you create a custom exception in C#?
Answer:
Create a custom exception by deriving a class from Exception and implementing appropriate constructors.
public class MyCustomException : Exception {
public MyCustomException(string message) : base(message) { }
}
32. What is the difference between throw and throw ex in C#?
Answer:
throw preserves the original stack trace, while throw ex resets the stack trace, making it harder to trace the original source of the exception.
try {
// Code that throws an exception
} catch (Exception ex) {
throw; // Preserves stack trace
}
33. How do you implement a try-finally block in C#?
Answer:
Use a try-finally block to execute code that must run whether or not an exception is thrown, such as resource cleanup.
try {
// Code that may throw an exception
} finally {
// Code that always runs
}
34. What is the purpose of the StackTrace class in C#?
Answer:
The StackTrace class provides information about the current call stack, useful for debugging and logging.
StackTrace st = new StackTrace();
Console.WriteLine(st.ToString());
35. How do you log exceptions in C#?
Answer:
Log exceptions by writing them to a file, database, or logging framework like log4net or NLog, typically inside a catch block.
try {
// Code that may throw an exception
} catch (Exception ex) {
File.WriteAllText(“log.txt”, ex.ToString());
}
36. How do you create a new thread in C#?
Answer:
Create a new thread using the Thread class, passing a ThreadStart delegate or lambda expression as the method to run.
Thread myThread = new Thread(new ThreadStart(MyMethod));
myThread.Start();
37. What is the Task class in C#, and how do you use it for asynchronous operations?
Answer:
The Task class represents an asynchronous operation. Use Task.Run() to execute a method asynchronously.
Task.Run(() => {
// Code to run asynchronously
});
38. How do you use the async and await keywords in C#?
Answer:
Mark a method with async and use await to asynchronously wait for the completion of a task.
public async Task<int> GetDataAsync() {
int result = await Task.Run(() => {
// Simulate long-running task
return 42;
});
return result;
}
39. What is a ThreadPool, and how do you use it in C#?
Answer:
A ThreadPool manages a pool of worker threads, reducing the overhead of thread creation. Use ThreadPool.QueueUserWorkItem() to queue tasks.
ThreadPool.QueueUserWorkItem(state => {
// Code to run in the thread pool
});
40. How do you implement a cancellation token to cancel an ongoing task in C#?
Answer:
Use the CancellationTokenSource and CancellationToken to signal and check for cancellation in a task.
CancellationTokenSource cts = new CancellationTokenSource();
Task.Run(() => {
while (!cts.Token.IsCancellationRequested) {
// Long-running task
}
}, cts.Token);
// Cancel the task
cts.Cancel();
41. How do you create a model class for a database table in Entity Framework?
Answer:
Define a C# class with properties corresponding to the database table columns, and annotate it with data annotations if needed.
public class Product {
public int ProductId { get; set; }
public string Name { get; set; }
}
42. How do you perform a basic CRUD operation using Entity Framework?
Answer:
Use the DbContext to perform Create, Read, Update, and Delete operations on the database.
using (var context = new MyDbContext()) {
var product = new Product { Name = “Laptop” };
context.Products.Add(product); // Create
context.SaveChanges();
var products = context.Products.ToList(); // Read
product.Name = “Updated Laptop”; // Update
context.SaveChanges();
context.Products.Remove(product); // Delete
context.SaveChanges();
}
43. What is lazy loading in Entity Framework, and how do you enable or disable it?
Answer:
Lazy loading delays the loading of related data until it is explicitly accessed. Enable or disable it using LazyLoadingEnabled in the DbContext.
context.Configuration.LazyLoadingEnabled = false;
[/su_note]
44. How do you handle database migrations in Entity Framework?
Answer:
Use Add-Migration and Update-Database commands in the Package Manager Console to handle schema changes and apply them to the database.
Add-Migration InitialCreate
Update-Database
45. How do you execute a raw SQL query in Entity Framework?
Answer:
Use the context.Database.SqlQuery<T>() method to execute a raw SQL query and return the result as a collection of entities.
var products = context.Database.SqlQuery<Product>(“SELECT * FROM Products”).ToList();
46. What is the Singleton pattern, and how do you implement it in C#?
Answer:
The Singleton pattern ensures a class has only one instance and provides a global point of access to it. Implement it using a private constructor and a static instance.
public class Singleton {
private static readonly Singleton instance = new Singleton();
private Singleton() { }
public static Singleton Instance {
get { return instance; }
}
}
47. How do you implement the Dependency Injection pattern in C#?
Answer:
Implement Dependency Injection by injecting dependencies through constructors, properties, or methods, often managed by an IoC container like Autofac or Unity.
public class MyClass {
private readonly IService _service;
public MyClass(IService service) {
_service = service;
}
}
48. What is the purpose of the SOLID principles in C# development?
Answer:
SOLID principles are guidelines for writing maintainable and scalable code, focusing on single responsibility, open-closed, Liskov substitution, interface segregation, and dependency inversion.
49. How do you implement the Factory Method pattern in C#?
Answer:
The Factory Method pattern defines an interface for creating an object but lets subclasses alter the type of objects that will be created.
public abstract class Creator {
public abstract IProduct FactoryMethod();
}
public class ConcreteCreator : Creator {
public override IProduct FactoryMethod() {
return new ConcreteProduct();
}
}
50. How do you ensure that a class implements multiple interfaces with the same method signature in C#?
Answer:
Use explicit interface implementation to ensure that each interface method is implemented separately, avoiding conflicts.
public class MyClass : IInterface1, IInterface2 {
void IInterface1.Method() {
// Implementation for IInterface1
}
void IInterface2.Method() {
// Implementation for IInterface2
}
}
Final Words
Getting ready for an interview can feel overwhelming, but going through these C# fresher interview questions can help you feel more confident.
With the right preparation, you’ll ace your C# interview but don’t forget to practice the C# basic syntax, object-oriented programming concepts, and .NET framework-related interview questions too.
Frequently Asked Questions
1. What are the most common interview questions for C#?
Common interview questions for C# typically focus on object-oriented programming, syntax, exception handling, and the .NET framework.
2. What are the important C# topics freshers should focus on for interviews?
Important C# topics freshers should focus on include classes and objects, inheritance, polymorphism, delegates, and LINQ.
3. How should freshers prepare for C# technical interviews?
Freshers should prepare for C# technical interviews by practicing coding problems, reviewing OOP principles, and understanding the .NET framework.
4. What strategies can freshers use to solve C# coding questions during interviews?
Freshers can use strategies like breaking down the problem, using proper OOP practices, and testing edge cases to solve C# coding questions during interviews.
5. Should freshers prepare for advanced C# topics in interviews?
Yes, freshers should prepare for advanced C# topics in interviews if the role demands in-depth knowledge or if specified in the job description.
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