40 C# Interview Questions for Freshers (2026, with Answers)

Imagine a recruiter from a Dallas insurance company books your first .NET phone screen for Monday: 30 minutes, “mostly C# basics.” You’ve got one weekend.

Most C# interview questions for freshers come from six areas: types, OOP, strings and collections, exceptions, LINQ and async basics, and modern C# features.

Quick answer: learn the 40 questions below, and run the five small .NET 10 programs so you can prove value vs reference, string immutability and == vs Equals.

What Does a Fresher C# Interview Look Like in 2026?

Most US companies hiring junior or entry-level .NET developers run three short rounds. Here’s what each one checks, so you can study for the right thing.

Round	Length	What they ask
Recruiter or phone screen	20-30 min	Rapid C# definitions, your projects, why .NET
Technical interview	45-60 min	“What does this print?” questions, OOP, collections, exceptions
Live coding	30-45 min	Reverse a string, find a prime, count words, in plain C#

I’ve grouped the questions in the same order interviewers usually go: from “What is C#?” up to C# 14. Each answer is short enough to say out loud in under a minute.

If you’ve already got two or more years of experience, this list is too easy. Jump to my C# interview questions for experienced developers instead, which goes into async internals, GC, and design rounds.

C# Basics and Data Types Interview Questions

1. What is C#?

C# is a modern, object-oriented, type-safe language from Microsoft. You use it to build web APIs, desktop apps, games with Unity, cloud services, and console tools.

The compiler checks types before the program runs, and the runtime manages memory for you. My longer answer to what C# is and where it’s used covers its history.

2. What’s the difference between C# and .NET?

C# is the language. .NET is the platform that runs it: the runtime, the base class libraries, and the SDK with the dotnet command.

In 2026 the current release is .NET 10, a long-term support (LTS) version, and it ships with C# 14. Say “.NET 10” rather than “.NET Framework” unless the job ad mentions legacy apps.

3. What are the CLR, IL, and JIT?

The compiler turns your C# into Intermediate Language (IL) inside an assembly, a .dll or .exe file. The Common Language Runtime (CLR) loads that assembly and runs it.

The just-in-time (JIT) compiler converts IL to machine code the first time a method runs. The CLR also handles garbage collection, type safety, and exceptions.

4. What’s the difference between value types and reference types?

A value type variable holds the data itself, so assigning it copies the data. A reference type variable holds a reference to an object, so assigning it copies only the reference.

This program shows both, plus what happens when you pass each one to a method:

int a = 10;
int b = a;              // copies the value
b = 25;
Console.WriteLine($"int:   a = {a}, b = {b}");

var c1 = new Cart { Items = 2 };
var c2 = c1;            // copies the reference
c2.Items = 5;
Console.WriteLine($"class: c1 = {c1.Items}, c2 = {c2.Items}");

Bump(a);
AddItem(c1);
Console.WriteLine($"after: a = {a}, c1 = {c1.Items}");

static void Bump(int n) => n++;
static void AddItem(Cart cart) => cart.Items++;

class Cart { public int Items; }

Output:

int:   a = 10, b = 25
class: c1 = 5, c2 = 5
after: a = 10, c1 = 6

Bump got a copy of a, so a stayed 10. AddItem got a copy of the reference, which points at the same Cart, so Items went from 5 to 6.

int, double, bool, decimal, enums, and structs are value types. Classes, records, arrays, strings, and delegates are reference types. Every built-in type is listed in my data types in C# guide.

5. When do you use decimal instead of double?

Use decimal for money and anything that must add up to the cent. Use double for measurements and science math, where speed matters more than exact decimal digits.

0.1 + 0.2 isn’t exactly 0.3 as a double, because it’s stored in binary. As 0.1m + 0.2m, it is.

6. What does var do?

var tells the compiler to infer the type from the right-hand side. It’s still static typing: var total = 19.99m; is a decimal forever.

You can’t use var without an initializer, and you can’t use it for fields. My variables in C# tutorial covers declarations and scope.

7. What’s the difference between const and readonly?

const is fixed at compile time and must be a number, bool, char, string, or null. readonly is set once at run time, in the declaration or a constructor, and works with any type.

8. What are nullable types, and what do ?? and ?. do?

int? lets a value type hold null, which is handy for an optional database column. ?? supplies a fallback when the left side is null, and ?. skips a member access on a null object.

With nullable reference types turned on, string? means “may be null,” and the compiler warns you before you dereference it. More patterns are in checking for null values in C#.

9. What’s the difference between implicit and explicit casting?

Implicit casting is automatic and safe, like int to long. Explicit casting needs a cast operator because data can be lost, like (int)19.99, which gives 19.

For text, use int.TryParse instead of int.Parse when the input might not be a number. Conversions and Convert methods are in type casting in C#.

10. What is a namespace?

A namespace groups related types and prevents name clashes, like System.Text for StringBuilder. A using directive at the top of a file lets you skip the prefix.

Modern projects use file-scoped namespaces (namespace Billing;) and implicit global usings. I explain both in namespaces in C#.

OOP Interview Questions in C# for Freshers

11. What’s the difference between a class and an object?

A class is the blueprint: fields, properties, and methods. An object is one instance of it in memory, created with new. Customer is a class; new Customer("Tyler Brooks") is an object.

12. What are the four pillars of OOP?

Encapsulation, inheritance, polymorphism, and abstraction. Give one sentence and one C# keyword for each, and you’ve answered better than most candidates.

Pillar	One-line answer	C# feature
Encapsulation	Hide data, expose behavior	private fields, properties
Inheritance	Reuse a base class	class Truck : Vehicle
Polymorphism	One call, many behaviors	virtual / override, overloading
Abstraction	Show what, hide how	abstract classes, interfaces

I walk through each pillar with one running example in OOP concepts in C#.

13. What is encapsulation, and what’s a property vs a field?

Encapsulation keeps an object’s data private and controls access through members. A field stores data; a property wraps it with get and set so you can validate values.

For example, a Balance property can refuse negative values while the field stays private. See encapsulation in C# for the full pattern.

14. What is inheritance, and does C# support multiple inheritance?

Inheritance lets a derived class reuse and extend a base class: class SavingsAccount : Account. A class can have only one base class.

C# gets the benefit of multiple inheritance through interfaces, since a class can implement many. My inheritance in C# tutorial shows the base and derived class rules.

15. What’s the difference between method overloading and overriding?

Overloading means the same method name with different parameters in one class, resolved at compile time. Overriding means a derived class replaces a virtual base method, resolved at run time.

Add(int, int) and Add(decimal, decimal) are overloads. The rules for each are in method overloading in C#.

16. What do virtual and override do?

virtual marks a base method as replaceable, and override supplies the new version in a derived class. The runtime picks the method from the object’s real type, not the variable’s type.

That’s runtime polymorphism. sealed stops further overriding. I show the call rules in method overriding in C#.

17. Abstract class or interface: what’s the difference?

An abstract class can hold fields, constructors, and finished methods, but a class inherits only one. An interface defines a contract, and a class can implement many.

I say it this way: use an abstract class for related types that share code, and an interface for a capability unrelated types share. Compare them in abstract class in C# and interface in C#.

18. What is abstraction?

Abstraction shows what an object does and hides how it does it. A PaymentProcessor exposes Charge(amount), and the caller never sees the card network code.

It’s the idea; abstract classes and interfaces are the tools. My abstraction in C# post separates the two.

19. What is a constructor?

A constructor is a method with the class’s name and no return type that runs when you create an object. It sets the starting state.

You can overload constructors, chain them with this(...), and add a static constructor that runs once per type. C# 12 added primary constructors: class Customer(string name). See constructors in C#.

20. What’s the difference between a struct and a class?

A struct is a value type and a class is a reference type. Structs can’t inherit from other structs or classes, and they suit small values like a point or a money amount.

Use a class by default. The structures in C# tutorial shows when a struct makes sense.

21. What do static and the access modifiers mean?

A static member belongs to the type, not an object, so you call Math.Max without new. A static class can’t be instantiated.

public is visible everywhere, private only inside the type, protected also in derived classes, and internal only inside the same assembly. Class members default to private.

C# String and Collection Interview Questions

22. Why are strings immutable in C#?

A string can’t change after it’s created. Methods like ToUpper and Replace return a new string, and the original stays the same. Freshers forget to keep the result:

string city = "Austin";
city.ToUpper();                  // the result is thrown away
Console.WriteLine(city);

string upper = city.ToUpper();   // keep the new string
Console.WriteLine(upper);

string saved = city;
city += ", TX";                  // builds a brand-new string
Console.WriteLine($"{saved} | {city}");

var sb = new System.Text.StringBuilder("Order");
sb.Append(" 1042").Append(" shipped");
Console.WriteLine(sb.ToString());

Output:

Austin
AUSTIN
Austin | Austin, TX
Order 1042 shipped

Immutability makes strings safe to share between threads and lets the runtime reuse literals. The cost is that += inside a loop creates a new string every pass.

23. String or StringBuilder: when do you use which?

Use string for text you build once or change a few times. Use StringBuilder when you append many times, such as in a loop, because it edits one buffer instead of creating new strings.

I timed both in string vs StringBuilder in C#.

24. What’s the difference between == and Equals?

For classes, both check reference equality unless the type changes that. Strings and records override them to compare content. The surprise comes when strings are typed as object:

string s1 = "Boston";
string s2 = string.Concat("Bos", "ton");    // built at run time
Console.WriteLine($"string ==     : {s1 == s2}");
Console.WriteLine($"string Equals : {s1.Equals(s2)}");

var c1 = new Customer("Jenna Morales");
var c2 = new Customer("Jenna Morales");
Console.WriteLine($"class ==      : {c1 == c2}");
Console.WriteLine($"class Equals  : {c1.Equals(c2)}");

var r1 = new CustomerRecord("Jenna Morales");
var r2 = new CustomerRecord("Jenna Morales");
Console.WriteLine($"record ==     : {r1 == r2}");

object o1 = s1, o2 = s2;
Console.WriteLine($"object ==     : {o1 == o2}");

class Customer(string name) { public string Name => name; }
record CustomerRecord(string Name);

Output:

string ==     : True
string Equals : True
class ==      : False
class Equals  : False
record ==     : True
object ==     : False

Strings compared as string return True both ways. Two Customer objects with the same name return False, but the record returns True because the compiler generates value equality.

The last line is the trap: typed as object, == compares references, and s2 was built at run time. For text, compare with string.Equals(a, b, StringComparison.OrdinalIgnoreCase). More options are in comparing strings in C#.

25. What’s the difference between an array and a List<T>?

An array has a fixed size set when you create it. A List<T> grows as you call Add and has handy methods like Remove, Contains, and Sort.

I use arrays for fixed data and lists for almost everything else. See arrays in C# and the C# List tutorial.

26. What is a Dictionary, and when do you use it?

A Dictionary<TKey,TValue> stores key-value pairs with fast lookup by key, like ZIP code to city. Keys must be unique, and the indexer throws KeyNotFoundException for a missing key.

Use TryGetValue when the key might not exist. My Dictionary in C# guide covers adding, updating, and looping.

27. for, foreach, while, or do-while: what’s the difference?

Use for when you need the index, foreach to visit every item in a collection, while to repeat while a condition holds, and do-while to run the body at least once.

break leaves the loop and continue skips to the next pass. The foreach loop in C# post explains why you can’t change a list while you loop over it.

28. What’s the difference between a switch statement and a switch expression?

A switch statement runs code blocks per case. A switch expression, added in C# 8, returns a value and reads like a lookup table: t switch { >= 300m => "free 2-day", _ => "$7.99" }.

Interviewers like seeing the expression form with relational patterns. The classic statement form is in switch case in C#.

Exception Handling Interview Questions for C# Freshers

29. How do try, catch, and finally work?

try holds code that might fail, catch handles a specific exception type, and finally always runs, failure or not. Put specific catches before general ones.

string[] inputs = ["42", "abc", "99999999999"];

foreach (string input in inputs)
{
    try
    {
        int qty = int.Parse(input);
        Console.WriteLine($"Parsed {qty}");
    }
    catch (FormatException)
    {
        Console.WriteLine($"'{input}' is not a number");
    }
    catch (OverflowException)
    {
        Console.WriteLine($"'{input}' is too big for int");
    }
    finally { Console.WriteLine("  finally ran"); }
}

Output:

Parsed 42
  finally ran
'abc' is not a number
  finally ran
'99999999999' is too big for int
  finally ran

Each input hit a different branch, and finally ran three times. In real code I’d use int.TryParse here, since bad input isn’t exceptional. More patterns are in try-catch in C#.

30. What’s the difference between throw and throw ex?

throw; rethrows the current exception and keeps the original stack trace. throw ex; resets the stack trace to that line, so you lose where the error started. Always use throw;.

31. What does the using statement do, and how does garbage collection work?

The garbage collector frees managed memory automatically once nothing references an object. It doesn’t close files or database connections on time, though.

That’s what using is for: it calls Dispose() at the end of the block, even after an exception. using var reader = new StreamReader(path); disposes at the end of the scope. Details are in dispose and finalize in C#.

32. Which exceptions do freshers hit most often?

Exception	Usual cause
NullReferenceException	Calling a member on a null variable
IndexOutOfRangeException	Array index below 0 or past Length – 1
FormatException	int.Parse on text that isn’t a number
DivideByZeroException	Integer division by zero
InvalidOperationException	Changing a list inside its foreach loop

Integer division by zero throws, but double division returns Infinity. I show both in division by zero in C#.

LINQ and Async Basics Interview Questions

33. What is LINQ?

Language Integrated Query lets you filter, sort, and total collections with methods like Where, Select, OrderBy, and Sum. The same syntax works on lists, XML, and databases through EF Core.

This program totals the Texas orders with LINQ, then picks a shipping tier per order with a switch expression:

using System.Globalization;
CultureInfo.CurrentCulture = new("en-US");

List<Order> orders =
    [new("TX", 120m), new("CA", 45.50m), new("TX", 310m)];

var tx = orders.Where(o => o.State == "TX").Sum(o => o.Total);
Console.WriteLine($"TX total: {tx:C}");

foreach (var o in orders)
    Console.WriteLine($"{o.Total,8:C} -> {Ship(o.Total)}");

static string Ship(decimal t) => t switch
{
    >= 300m => "free 2-day",
    >= 100m => "free ground",
    _ => "$7.99 ground",
};

record Order(string State, decimal Total);

Output:

TX total: $430.00
 $120.00 -> free ground
  $45.50 -> $7.99 ground
 $310.00 -> free 2-day

The two Texas orders total $430.00. Note the en-US culture line: without it, :C prints in the computer’s local currency.

34. What’s deferred execution in LINQ?

Most LINQ operators don’t run when you write the query. They run when you loop over it or call ToList(), Count(), or Sum(), and they run again each time.

For a fresher answer, that’s enough. Call ToList() once if you’ll use the result more than once.

35. What do async and await do?

async marks a method that contains await. At an await on a slow operation, like a web request, the method gives the thread back and continues when the result is ready.

The app stays responsive and a web server can handle more requests. Return Task or Task<T>, and avoid async void except for event handlers.

36. What’s the difference between a Task and a Thread?

A Thread is an operating-system thread you manage yourself. A Task is a unit of work that the runtime schedules, usually on the thread pool, and it can return a result.

Modern code uses tasks with async/await. You’ll rarely create a Thread directly.

37. What are delegates and events?

A delegate is a type-safe variable that holds a method, so you can pass behavior around. Func returns a value, and Action returns nothing.

An event is a delegate that outside code can only subscribe to with += or unsubscribe from with -=. See delegates in C# and events in C#.

Modern C# 12, 13, and 14 Questions Freshers Get in 2026

38. What is a record?

A record is a type built for data, with value equality generated for you. record Order(string State, decimal Total); gives you a constructor, read-only properties, ToString, and == that compares values.

Use with to copy a record with one change: order with { Total = 99m }. You saw record equality in question 24.

39. What are pattern matching and switch expressions used for?

Pattern matching tests a value’s type or shape and pulls data out in one step: if (shape is Circle c). Relational patterns like >= 300m replace long if/else chains, as in the Ship method above.

40. What’s new in C# 14 and .NET 10?

C# 14 ships with .NET 10. Know three features: the field keyword for property accessors, null-conditional assignment (customer?.Order = order;), and extension members, which add extension properties.

.NET 10 also lets you run a single file with dotnet run app.cs, the way I ran every program here. My What’s new in C# 14 roundup has a runnable example for each feature.

Common Mistakes Freshers Make in C# Interviews

These cost more points than not knowing an answer:

• Saying “value types live on the stack.” A struct field inside a class lives on the heap. Say “value types are copied” instead.
• Memorizing definitions without code. Interviewers follow up with “show me.” Practice writing each answer in a few lines.
• Mixing up C# and .NET versions. C# 14 is the language; .NET 10 is the platform.
• Freezing in live coding. Talk through your plan first, then write the simple version. A working loop beats a clever one-liner that fails.

For live coding warm-ups, I’d practice reversing a string in C# and the prime number check in C#. Both show up in fresher rounds all the time.

Which C# Interview Topics Should Freshers Study First?

If you’ve only got a weekend, spend it on questions 4, 17, 22, 24, and 29. Value vs reference, abstract class vs interface, strings, equality, and exceptions come up in almost every fresher screen.

Then set up the VS Code console app setup and run the five programs above. Change one line, predict the output, and check yourself.

A few more posts help with the follow-up questions:

• Interface tricks in multiple inheritance in C#
• Wrapping values in boxing and unboxing in C#
• Named constants with enum in C#
• Web API questions in .NET Core interview questions

Frequently Asked Questions