Top 41 C# Interview Questions and Answers

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07/Jul/2020 | 10 minutes to read

Best Answers to C# Interview Questions

QFLES is listing some Essential C# Interview Questions and Answers for Freshers and mid level of Experienced Professionals prepared by Industry Experts. All answers for these C# interview questions are given based on standard documents and tried to explain in simple and easiest way.

1. What is latest version of C# with features?

C# 1.0 released in 2002. Like other languages Microsoft is also releasing it's new versions every year. Latest Version of C# is 8.0. For more you can visit Microsoft official site Releases . There are many new features in C# 8.0. You can go through Here.

2. Differentiate const vs readonly vs static

Constant

ReadOnly

Static

3. Differentiate in vs ref vs out

In

Ref

Out

4. What is Inheritance? Why C# does not support multiple Inheritance?

To understand this you need to understand the Diamond problem first:
The Diamond problem (sometimes referred to as the "deadly diamond of death") is an ambiguity that arises when two classes B and C inherit from Class A and class D inherits from both B and C. If a method in D calls a method defined in A(and does not override the method), and B and C have overridden that method differently, then from which class does it inherit: B or C?

5. What is Shadowing or Hiding?

Shadowing

class BC
{
  public void Display()
  {
     System.Console.WriteLine("BC::Display");
  }
}

class DC : BC
{
  public void Display()
  {
     System.Console.WriteLine("DC::Display");
  }
}

class Demo
{
  public static void Main()
  {
     DC obj = new DC();
     obj.Display();
  }
}

Output : DC:Display

class DC : BC
{
  new public void Display()
  {
     System.Console.WriteLine("DC::Display");
  }
}

6. What is the difference between Var, Object and Dynamic keywords?

I am giving one example from this you will understand the differences.

class Program
    {
        static void Main(string[] args)
        {
            var x = 10;
            object y = 20;
            dynamic z = 30;

            x = "bhanu"; // Error -  Cannot implicitly convert type 'string' to 'int'

            y = "bhanu";
            y = y - 10;  //Error Operator '-' cannot be applied to operands of type 'object' and 'int'

                   z = "bhanu";
            z = z - 10;
            Console.WriteLine("{0},{1},{2}",x,y,z);
            Console.ReadLine();
        }

        void disp(var x) // Error CS0825  The contextual keyword 'var' may only appear within a local variable declaration or in script code
        {

        }
        void disp(object x)
        {

        }
        void disp1(dynamic x)
        {

        }
    }

var

object

dynamic

7. Can Virtual or Abstract member be declare private ?

No, It will throw compile time error.

virtual void display() // will throw error here
        {
        // Implementation

        }

8. What is Boxing and Unboxing in C# ?

Boxing

UnBoxing

int a = 13;
            // The below line boxes i.
            object o = i; 
The object o can then be unboxed and assigned to integer variable i:
o = 13;
            a = (int)o;  // unboxing

9. What is Method Overloading?

When you define a method with same name but different method signature in a class is called method overloading. Method Signature does not include method return type.
For method overloading you can use different types of parameters or different sequence of parameters or different number of parameters.
Method overloading example:

        void display(int x)
        {
        // Implementation
        }
        void display(float x)
        {
            // Implementation
        }
        void display(int x, int y)
        {
            // Implementation

        }

10. What are Value Type and Reference Type?

Value Types

• All numeric data types
• Boolean, Char, and Date
• All structures, even if their members are reference types
• Enumerations, since their underlying type is always SByte, Short, Integer, Long, Byte, UShort, UInteger, or ULong

Reference types

11. What is Abstraction and Encapsulation? How these are different from each other?

Abstraction and Encapsulation both are the OOPs concept. Let's look into these.

Abstraction

Encapsulation

Main difference between encapsulation and abstraction:

• Abstraction is achieved at design level but Encapsulation is achieved at Implementation level.
• Abstraction is about to show only relevant information, Encapsulation is about putting related things into a single unit.

12. What is the deference between Interface and Abstract class? What is the need of these?

Abstract class and Interface both are used to implement a abstraction layer.

Abstract

Interface

Differences and why each is required?

• Interface is required to implement multiple inheritance concept in c# as Abstract class does not support it.
• Interface does not contain data members and constructors but Abstract class contains data members and constructors.
• Interface contains only incomplete members but Abstract class contains both incomplete(abstract) and complete members.
• Members of Interface can not be static but complete members of Abstract class can be static.

Need of Interface

13. What is Polymorphism? Describe the static and Dynamic Polymorphism?

14. What will be output of below program? 'Error Line' will throw any error?

  class A
    {
       public virtual void display()
        { Console.WriteLine("A - display"); }
    }
    class B:A
    {
        public override void display()
        { Console.WriteLine("B - display"); }
    }
    class Test
    {
        static void Main()
        {
            A obj = new A();
            obj.display();

            A obj1 = new B();
            obj1.display();

            B o = new B();
            o.display();
            // B ob = new A();  Error Line
            Console.ReadLine();
        }
    }

Output: 'Error Line' will throw error - Cannot implicitly convert type 'A' to 'B'. An explicit conversion exists (are you missing a cast?).
Output will be as below.
A - display
B - display
B - display

16. Can Abstract class has constructor? Below code will compile or not, or it will give any error in Error line 1 or 2.

class A
    {
       public virtual void display()
        {
            Console.WriteLine("A - display");
        }
        public virtual void disp()
        {
            Console.WriteLine("A - disp");
        }
    }
abstract class ab :A
    {
        public ab()
        { }
        public abstract override void display(); Error Line 1

        public sealed override void disp()  Error Line 2
        {
            Console.WriteLine("disp is sealed now.");
        }
    }

Solution: Abstract class can contain the constructor. Constructor is used to instantiate the class instance members.
Above code will compile successfully. We can add Abstract and Sealed keywords with the override keyword.

17.

18.

Some General Interview Questions for C#:

1. How much will you rate your self in C#?

When you attend an interview, Interviewer may ask you to rate your self in specific Technology like C#, So It's depend on your knowledge and work experience in C#.

2. What challenges did you face while working on C#?

This question may be specific to your technology and completely depends on your past work experience. So you need to just explain the challenges you faced related to C# in your Project.

3. What was your role in last Project related to C#?

It's based on your role and responsibilities assigned to you and what functionality you implemented using C# in your project. This question is generally asked in every interview.

4. How much experience do you have in C#?

Here you can tell about your overall work experience on C#.

5. Have you done any C# Certification or Training?

It's depend on candidate like you have done any C# training or certification. Certifications or trainings are not essential but good to have.