C# Interview Questions

31. What are Custom Exceptions?

Sometimes there are some errors that need to be handled as per user requirements. Custom exceptions are used for them and are used defined exceptions.

32. What are delegates?

Delegates are same are function pointers in C++, but the only difference is that they are type safe, unlike function pointers. Delegates are required because they can be used to write much more generic type-safe functions.

33. How do you inherit a class into other class in C#?

Colon is used as inheritance operator in C#. Just place a colon and then the class name.

public class DerivedClass : BaseClass

34. What is the base class in .net from which all the classes are derived from?


35. What is the difference between method overriding and method overloading?

In method overriding, we change the method definition in the derived class that changes the method behavior. Method overloading is creating a method with the same name within the same class having different signatures.

36. What are the different ways a method can be overloaded?

Methods can be overloaded using different data types for a parameter, different order of parameters, and different number of parameters.

37. Why can’t you specify the accessibility modifier for methods inside the interface?

In an interface, we have virtual methods that do not have method definition. All the methods are there to be overridden in the derived class. That’s why they all are public.

38. How can we set the class to be inherited, but prevent the method from being over-ridden?

Declare the class as public and make the method sealed to prevent it from being overridden.

39. What happens if the inherited interfaces have conflicting method names?

Implement is up to you as the method is inside your own class. There might be a problem when the methods from different interfaces expect different data, but as far as compiler cares you’re okay.

40. What is the difference between a Struct and a Class?

Structs are value-type variables, and classes are reference types. Structs stored on the Stack causes additional overhead but faster retrieval. Structs cannot be inherited.

41. How to use nullable types in .Net?

Value types can take either their normal values or a null value. Such types are called nullable types.

Int? someID = null;

42. How we can create an array with non-default values?

We can create an array with non-default values using Enumerable.Repeat.

43. What is difference between “is” and “as” operators in c#?

“is” operator is used to check the compatibility of an object with a given type, and it returns the result as Boolean.

“as” operator is used for casting of an object to a type or a class.

44. What’s a multicast delegate?

A delegate having multiple handlers assigned to it is called multicast delegate. Each handler is assigned to a method.

45. What are indexers in C# .NET?

Indexers are known as smart arrays in C#. It allows the instances of a class to be indexed in the same way as an array.


public int this[int index]    // Indexer declaration

46. What is difference between the “throw” and “throw ex” in .NET?

“Throw” statement preserves original error stack whereas “throw ex” have the stack trace from their throw point. It is always advised to use “throw” because it provides more accurate error information.

47. What are C# attributes and its significance?

C# provides developers a way to define declarative tags on certain entities, eg. Class, method, etc. are called attributes. The attribute’s information can be retrieved at runtime using Reflection.

48. How to implement a singleton design pattern in C#?

In a singleton pattern, a class can only have one instance and provides an access point to it globally.


Public sealed class Singleton
Private static readonly Singleton _instance = new Singleton();

49. What is the difference between directcast and ctype?

DirectCast is used to convert the type of object that requires the run-time type to be the same as the specified type in DirectCast.

Ctype is used for conversion where the conversion is defined between the expression and the type.

50. Is C# code is managed or unmanaged code?

C# is managed code because Common language runtime can compile C# code to Intermediate language.

51. What is Console application?

A console application is an application that can be run in the command prompt in Windows. For any beginner on .Net, building a console application is ideally the first step, to begin with.

52. Give an example of removing an element from the queue

The dequeue method is used to remove an element from the queue.

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

namespace DemoApplication
 class Program
  static void Main(string[] args)
   Queue qt = new Queue();

   foreach (Object obj in qt)
    Console.WriteLine(); Console.WriteLine();
    Console.WriteLine("The number of elements in the Queue " + qt.Count);
    Console.WriteLine("Does the Queue contain " + qt.Contains(3));