This list of C# interview questions for freshers covers everything you need to walk into a 2026 interview with confidence. C# remains one of the most in-demand languages for enterprise, game, and web development, and freshers who prepare with the right C# interview questions for freshers stand out quickly from candidates who rely only on classroom knowledge.
In this guide:
-> C# Interview Questions on Language Fundamentals and Type System (Q1–5)
-> Access Modifiers and Object Setup (Q6–10)
-> OOP-Based C# Interview Questions for Freshers — Questions 11 to 20
-> LINQ Interview Questions for Freshers: Lambda Basics (Q25–27)
-> Exception Handling — Questions 31 to 35
-> Async Programming and Threading — Questions 36 to 40
-> Advanced C# Interview Questions for Freshers— Questions 41 to 50
C# Interview Questions on Language Fundamentals and Type System (Q1–5)
1. What is C# and what are its main features? C# is an object-oriented, type-safe language from Microsoft, part of .NET. It’s used for desktop apps, web APIs, mobile apps, Unity games, and cloud services. Key features: garbage collection, strong type safety, LINQ, and async/await.
2. Managed vs. unmanaged code? Managed code runs under the Common Language Runtime (CLR), which handles memory and exceptions automatically. Unmanaged code (like C/C++) requires manual memory management. C# code is managed by default.
3. Value types vs. reference types? Value types (int, bool, struct) store data directly and live on the stack; copying creates an independent copy. Reference types (class, string, array) store a pointer to heap data; copying shares the same object.
4. What is boxing and unboxing? Boxing wraps a value type in an object; unboxing extracts it back. Boxing allocates heap memory, so it’s slower — avoid it in performance-critical code.
int x = 42;
object boxed = x; // boxing
int unboxed = (int)boxed; // unboxing5. == vs. .Equals()? For value types, both compare values identically. For reference types, == checks memory location by default, while .Equals() can be overridden to compare content — string does exactly this.
Access Modifiers and Object Setup (Q6–10)
6. What are access modifiers? public (anywhere), private (same class), protected (class + subclasses), internal (same assembly), protected internal (either), private protected (subclasses in the same assembly).
7. const vs. readonly? const is fixed at compile time and never changes. readonly can be set in a constructor and stays fixed afterward — useful when the value depends on runtime input.
const double Pi = 3.14159;
readonly int maxRetries;
public MyClass(int retries) { maxRetries = retries; }8. What constructor types exist? Default (no parameters), parameterised, copy (accepts another object of the same class), static (runs once before any instance), and private (blocks external instantiation, common in singletons).
9. string vs. StringBuilder? string is immutable — every change creates a new object. StringBuilder mutates in place, making it faster for loops and repeated concatenation.
10. What is a nullable type? It lets a value type hold null, using ? after the type — useful for optional data like a database column.
int? age = null;
if (age.HasValue) Console.WriteLine(age.Value);
else Console.WriteLine("Age not provided");OOP-Based C# Interview Questions for Freshers — Questions 11 to 20
Core OOP Principles (Q11–13)
11. The four pillars of OOP in C#? Encapsulation (bundling data/behavior, restricting access), inheritance (: syntax reuses a parent class), polymorphism (overriding/overloading), and abstraction (abstract classes and interfaces hiding implementation).
12. Abstract class vs. interface? An abstract class can mix implemented and abstract methods, fields, and constructors — a class inherits only one. An interface defines a contract (with optional default implementations since C# 8) — a class can implement many. Use an abstract class for shared logic, an interface for unrelated classes needing a common contract.
13. Overloading vs. overriding? Overloading: same method name, different parameters, resolved at compile time. Overriding: a derived class redefines a virtual base method using override, resolved at runtime.
Sealed and Static Classes (Q14–15)
14. What is a sealed class? It blocks further inheritance, slightly improves performance, and is often used for security when behavior must not change — string is a real example.
15. What is a static class? It contains only static members, can’t be instantiated with new, can’t inherit another class, and can’t implement an interface. Good for stateless utilities, like Math.
Delegates, Generics, and Extension Methods (Q16–20)
16. Delegate vs. event? A delegate is a type-safe method reference, like a function pointer. An event wraps a delegate but only lets external code subscribe/unsubscribe — only the declaring class can raise it.
delegate void Notify(string message);
Notify n = Console.WriteLine;
n("Hello from delegate");17. What are generics and why use them? Generics give type-safe code without casting, reduce boxing, and catch errors at compile time. List<T> and Dictionary<TKey, TValue> are common examples.
18. What is a partial class? It splits one class’s definition across multiple files, merged at compile time — handy for keeping auto-generated code separate from custom logic.
19. Early binding vs. late binding? Early binding resolves calls at compile time (faster, with IntelliSense). Late binding resolves at runtime (via dynamic or reflection) — more flexible but slower.
20. What are extension methods? They add new methods to existing types without modifying the source, defined as static methods using this before the first parameter.
public static class StringExtensions
{
public static bool IsNullOrEmpty(this string value)
=> string.IsNullOrEmpty(value);
}
// Usage: "hello".IsNullOrEmpty();
LINQ Interview Questions for Freshers: Lambda Basics (Q25–27)
Choosing the Right Collection (Q21–24)
21. Array vs. List vs. ArrayList? Array is fixed-size and typed. List<T> is generic, resizable, and type-safe. ArrayList is the older, non-generic version requiring casting — avoid it in modern code.
22. Dictionary vs. Hashtable? Dictionary<TKey, TValue> is generic, type-safe, and faster. Hashtable is older, non-generic, and needs casting. Use Dictionary today.
23. IEnumerable vs. IQueryable? IEnumerable filters in memory after loading all data. IQueryable pushes filtering to the data source (e.g., SQL), reducing data transferred over the network.
24. Stack vs. Queue? Stack is LIFO (Push/Pop) — good for undo operations. Queue is FIFO (Enqueue/Dequeue) — good for task scheduling.
Lambda Expressions and LINQ Basics (Q25–27)
25. What is a lambda expression? A short anonymous function using =>, commonly passed to LINQ methods and delegates.
Func<int, int> square = x => x * x;
Console.WriteLine(square(5)); // 2526. What is LINQ? Language Integrated Query lets you query collections, databases, and XML using C# syntax, in either method syntax (common in production) or SQL-like query syntax.
var result = numbers.Where(n => n > 5).OrderBy(n => n).Select(n => n * 2).ToList();27. First() vs. FirstOrDefault()? First() throws if nothing matches. FirstOrDefault() returns a default value (null/0) instead — use it when a missing match is a valid outcome.
Deferred Execution and Query Methods (Q28–30)
28. What is deferred execution? A LINQ query doesn’t run when defined — only when enumerated (foreach, ToList()). This means it reflects the latest data if the source changes before execution.
29. Select() vs. SelectMany()? Select() projects each item into a new form. SelectMany() flattens nested collections into one list.
var allItems = orders.SelectMany(o => o.Items).ToList();30. Any() vs. All()? Any() is true if at least one element matches. All() is true only if every element matches.
bool hasAdult = people.Any(p => p.Age >= 18);
bool allAdults = people.All(p => p.Age >= 18);Exception Handling — Questions 31 to 35
Try-Catch-Finally and Rethrowing (Q31–32)
31. Purpose of try, catch, and finally? try holds risky code, catch handles specific exception types, and finally always runs — ideal for cleanup like closing files or connections.
32. throw vs. throw ex? throw rethrows while preserving the original stack trace. throw ex resets it, hiding where the error started. Always prefer plain throw in a catch block.
catch (Exception ex)
{
throw; // preserves stack trace
}Custom Exceptions and Common Errors (Q33–34)
33. What is a custom exception? A class extending Exception, used when built-in exceptions don’t convey enough business-specific meaning.
public class InsufficientFundsException : Exception
{
public decimal Amount { get; }
public InsufficientFundsException(decimal amount)
: base($"Insufficient funds: {amount} required") => Amount = amount;
}34. Common built-in exceptions? NullReferenceException (null member access), IndexOutOfRangeException (bad array index), InvalidCastException (bad conversion), StackOverflowException (deep recursion), OutOfMemoryException, DivideByZeroException, and ArgumentNullException.
Resource Cleanup with using (Q35)
35. What does the using statement do? It ensures an IDisposable object’s Dispose() runs automatically when it goes out of scope, even after an exception — essentially syntactic sugar for try-finally.
using (var reader = new StreamReader("file.txt"))
{
string content = reader.ReadToEnd();
} // Dispose() called automaticallyAsync Programming and Threading — Questions 36 to 40
C# Interview Questions on Async/Await Fundamentals (Q36–38)
36. async vs. await? async marks a method as asynchronous, enabling await inside it. await pauses that method without blocking the calling thread, resuming once the task completes.
public async Task<string> GetDataAsync()
{
string data = await FetchFromApiAsync();
return data;
}37. Task vs. Thread? Thread directly creates an OS thread with manual management. Task is a higher-level abstraction using the thread pool, with built-in cancellation and continuations — prefer Task in modern code.
38. What causes deadlock in async code, and how do you avoid it? Deadlock often happens when calling .Result or .Wait() on a task inside a context with a synchronization context (ASP.NET, UI threads), where the resumed method waits on the same blocked thread. Avoid mixing blocking calls with await.
Running Tasks in Parallel (Q39–40)
39. What is Task.WhenAll()? It runs multiple independent tasks concurrently and waits for all to finish — faster than awaiting them one by one.
var task1 = FetchUserAsync();
var task2 = FetchOrdersAsync();
await Task.WhenAll(task1, task2);40. What is CancellationToken? It signals a running async operation to stop, checked periodically inside long-running methods — useful when a user navigates away mid-request.
public async Task DoWorkAsync(CancellationToken token)
{
for (int i = 0; i < 100; i++)
{
token.ThrowIfCancellationRequested();
await Task.Delay(100, token);
}
}Advanced C# Interview Questions for Freshers— Questions 41 to 50
Advanced C# Interview Questions: Interfaces and Delegate Types (Q41–42)
41. IEnumerable vs. ICollection vs. IList? IEnumerable supports forward-only iteration. ICollection adds Count, Add, Remove. IList adds index access and Insert/RemoveAt. Use the least capable interface your code actually needs.
42. Func vs. Action vs. Predicate? Func returns a value, Action returns void, and Predicate takes one parameter and returns bool — all built-in shortcuts avoiding custom delegate types.
Func<int, int, int> add = (a, b) => a + b;
Action<string> print = s => Console.WriteLine(s);
Predicate<int> isEven = n => n % 2 == 0;Design Patterns and Copying Objects (Q43–44)
43. How do you implement Singleton in C#? Use Lazy<T> for thread-safe, lazy initialization without manual locking.
public class Singleton
{
private static readonly Lazy<Singleton> instance = new(() => new Singleton());
private Singleton() { }
public static Singleton Instance => instance.Value;
}44. Shallow copy vs. deep copy? A shallow copy shares nested reference objects with the original. A deep copy duplicates nested objects too, so changes to one don’t affect the other — typically done via serialization or manual copying.
Attributes and Reflection (Q45–46)
45. What are attributes? Metadata tags applied with [ ] to classes, methods, or properties — like [Obsolete], [Serializable], or [HttpGet]. You can also define custom attributes.
46. What is reflection? It lets you inspect and invoke type information at runtime — used by DI frameworks, serializers, and ORMs. It’s slower than direct code, so use it only when runtime discovery is genuinely needed.
Type Checking and Variance (Q47–48)
47. is vs. as? is checks type compatibility and returns bool. as attempts a cast and returns null on failure instead of throwing.
if (obj is Student s) Console.WriteLine(s.Name);
var student = obj as Student;48. Covariance vs. contravariance? Covariance (out) allows a more derived type where a less derived one is expected — e.g., IEnumerable<Dog> assignable to IEnumerable<Animal>. Contravariance (in) allows the reverse for input parameters.
Disposal and Dependency Injection (Q49–50)
49. What is the IDisposable pattern? It provides Dispose() to release unmanaged resources, typically via a public Dispose() calling a protected Dispose(bool), plus a finalizer as a safety net. Pair it with using.
50. What is dependency injection? A pattern where a class receives dependencies from outside instead of creating them, improving testability and reducing coupling. ASP.NET Core’s built-in DI container supports three lifetimes: Singleton, Scoped, and Transient.
builder.Services.AddScoped<IUserService, UserService>();
public class UserController
{
private readonly IUserService _service;
public UserController(IUserService service) => _service = service;
}Final Thoughts
These 50 C# interview questions for freshers cover what an interviewer expects to test in 2026, from syntax and OOP through async programming and dependency injection. Focus first on your weakest sections, practice explaining answers out loud, and type out every code example yourself rather than memorizing it. If you want structured, guided practice instead of going it alone, FPC’s training programs are built to help freshers get interview-ready faster. Interviewers value clear thinking far more than a perfectly worded textbook answer.
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