MUST Have C# Interview Questions and Answers – Part 2

This C# Tutorial Part-2 in series of C# Interview Questions with practical and detailed answers. In previous part, we covered many basic to intermediate level interview questions on C# with the help of practical examples. I’ll recommend strongly to go through part-1 in this series. We will continue this series to provide more practical details with real time scenarios and complete source code to grasp C# language concepts. But this time, we are understanding in a different way by comparing different concepts.Image may be NSFW.
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C# Interview Questions PDF version will be available later for download.

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Following Technical Interview Questions and Answers will also be helpful.

• C# Interview Questions – Part-1
• ASP.NET Interview Questions Part-1 [Basics, Controls, State Management]
• ASP.NET Interview Questions Part-2 [Advanced Controls, Globalization and Localization]
• ASP.NET Interview Questions Part-3 [Caching & Security etc.]
• ASP.NET Interview Questions Part-4 [Advance Security]
• ASP.NET Interview Questions Part-5 [ASP.NET AJAX]
• ASP.NET Interview Questions Part-6 [ASP.NET Web API]
• ASP.NET MVC Interview Questions
• Entity Framework Interview Questions

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Complete C# Interview Questions List

• Managed Vs Unmanaged Code
• Struct Vs class
• Abstract Vs Interface
• Boxing Vs Unboxing
• Method Overloading Vs Method Overriding
• Break and Continue Statements
• Constant Vs Read-Only
• Ref and out parameters
• String Vs String Builder
• Array.copyTo() Vs Array.Clone()
• Dispose and Finalise methods
• Late binding Vs Early binding
• IEnumerable & Iqueryable
• Throw Exception Vs Throw Clause
• == Vs equals
• Is Vs as operator
• Array Vs Array List
• Directcast Vs ctype
• Public Vs Static Vs void

Managed Vs Unmanaged Code

Managed Code:

The code (like Vb.Net,C#,J#) which is written in .Net Framework and developed by .Net Framework and under the control of CLR(Common Language Runtime). And the garbage collector run automatically in managed code.

Unmanaged Code:

The code which is developed outside of the .Net framework is called unmanaged code. Unmanaged code does not run under the control of CLR. Unmanaged code executed with help of wrapper class CCW (COM Callable Wrapper) and RCW(Runtime Callable Wrapper). C++ can be used to write such application.

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Struct Vs class

Structs and classes are the template or blue print that is used to create an object of a class.

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Abstract Vs Interface

Abstract class and interface both are used to achieve abstraction (for hiding the functionality). Both contain the abstract method.

Example of an Abstract class:

namespace ConsoleApplication
{
   abstract class A                  // contain method body
   {
      public int add(int a,int b)   
      {
          return a+b;
      }
   }

   class B : A       //classs B extends class A
   {
     public int mul(int a,int b)
      {
         return a*b;
      }
   }

   class TestMain
   {
      Static void Main(string[] args)
      {
         B ob=new B();
         int result=ob.add(5,10);
         Console.WriteLine(“result {0}”,result);
         Console.ReadLine();
      } 
   }
}

Example of Interface:

namespace ConsoleApplication
{
   interface A          // can not contain method body
   {
      void method();    //public abstract by default
   }

   class B : A          // class B implements interface A
   {
      Void mehtod()
      {
            Console.WriteLine(“Hello Welcome”);
            Console.ReadLine();
      }

      Static void main(string[] args)
      {
         B ob=new B();
         ob.mehod();
      }
    }    
}

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Boxing Vs Unboxing

In C# there is three types of data type Value type,Reference Type and pointer type. The process of the converting a value type into reference type is called Boxing. While the Reference type is converting into value type called unboxing.

Int a=5;
Object obj=5;    //Boxing
Int a=(Int)obj;    //Unboxing

Example of Boxing and Unboxing:

namespace ConsoleApplication1
{
      internal class Program
      {
         private static void Main(string[] args)
         {
             double a;
             object ref;
             a = 100;

             ref = a;            //Boxing - Value type to Object
             double result = (double)ref;   // UnBoxing - Reference Type to Value
             Console.WriteLine(Result);   // 100
             Console.ReadLine();  
         }
      }
}

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Method Overloading Vs Method Overriding

Example of Method Overloading:

namespace ConsoleApplication
{
    class Calculation
    {
        public void add(int a,int b)
        {
           Console.WriteLine(a+b);
        }
        public void add(int a,int b,int c)
        {
          Console.WriteLine(a+b+c);
        }
    }
    class TestMain
    {
       static void Main(string[] args)
       {
             Calculation ob=new Calculation();
             ob.add(5,10);
             ob.add(5,10,15);
       }
    }
}

Example of Method Overriding:

namespace ConsoleApplication
{
    class A
    {
        public virtual void Method()                                // Virtual method
        {
            Console.WriteLine("This is the Base Class");
        }
    }

    class B : A
    {
        public override void Method()                                // Overriding virtual method 
        {
            Console.WriteLine("This is the Derived Class");
        }
    }

    class TestMain
    {
        static void Main()
        {
           B ob=new B();
           ob.Method();//                   output:  This is Derived Class
        }
    }
}

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Break and Continue Statements

Break statement is used to break out of loop that’s mean you can jump out of loop at the current position and it terminate the loop.

Continue statement is used to (one iteration) jump over one iteration and again it continues the loop.

namespace ConsoleApplication
{
    class A
    {
        static void Main(string[] args)
        {
 
          int i;          
          for (i = 0; i <= 10; i++)
          { 
              if (i == 4)                // it jump out of loop where i==4  and start again from next value      
                  continue;
             
              if (i == 7)              // iteration stoped when i==7 and terminate the program
                  break; 
              Console.WriteLine(i);            
          } 
          Console.ReadLine();              
        }    
    }
}

Output:
0
1
2
3
5
6

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Constant Vs Read-Only

Constant and Read-only is the keyword that is used to make the field constant that can not be modified.

Constant Value:

Constant variable or local variable are assigned at the time of declaration they cannot be modified after the declaration. Constant variables are static by default hence you cannot use static keyword with the constant field (or variable).

public const int a=1;

ReadOnly:

A read-only field can be assigned either at the time of declaration or inside the constructor of the same class, that’s why read only field can be used run-time constant.

class A
{
  readonlyint a=1;
  readonlyint b

  public A(int a)
  {
    this.a=a;
  }
}

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Ref and out parameters

Ref and out parameters are used to pass an argument into a method. By using this parameter you can return more than one value.

In the case of ref parameter first you need to initialize it then pass to the method but for out parameter, you don’t need to initialize.

Ref:

The ref keyword is used to pass an argument as a reference. When the value of that parameter will be changed in the method, it will be reflected in the calling method.

It needs to be initialized before passing into the method.

class A()
{
    Static void Main()
    {
       Int a;     //need to be initialised
       a=1;

       method(ref a)
       Console.Write(a);
    }

    public static void method(ref int b)
    {
        B+=5;
    }
}

Output: 6

Out:

The out keyword is used to pass an argument same as ref keyword but in the case of out ref, you can pass the argument without assigning the value. Instead, it must be initialized in the called method before it returns back to the calling method.

class A
{
    Static void Main()
    {
        Int a,b;         // no need to be initialised
        Method(out a, out b)
        Console.Write(a);
        Console.Write(b);
    }

    Public static intmethod(out int n, out int m)
    {
       n=2;
       m=5;
       return 0;
    }
}  

Output:
2
5

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String Vs String Builder

String:

String is Reference type data type, you cannot insert, modify or delete any data when a string is created that means in simple word we can say that string is an immutable means once you created the object of string you cannot modify it when you try to modify it will create a new object in memory.

String s1= “Hello Jackson”;
String s1=”Hye Jackson”;      // created a new object

String Builder:

String Builder is an object of string to work with string we have to use a namespace(“Using System. Text) so unlike string, a string builder is an object and we can apply insert, modify and remove function in string builder without creating a new object, It will automatically update in memory does not create new space in memory. We can also say that string builder is mutable that’s mean changeable.

StringBuildersb=new StringBuilder();
sb.append(“Hello jackson”);
sb.replace(“hiijackson”);     //updating string memory

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Array.copyTo() Vs Array.Clone()

Array.copyTo () and Array. Clone() both areused to replicate the element of existing Single dimension array.

Array.copyTo:

Array.copyTo () method copy the array’s element into existing/destination array with the reference of targeted instance of existing/destination array. You can say that Array.copyTo allows to replicate the into specified index.

Array.Clone():

Array. Clone () replicate the existing element array in the new array object containing all element of exiting array without having any reference.

using system;

class copycloneexp
{
   public static void Main()
   {

      Int[] existingarray=new int[3];
      existingarray[0]=10;
      existingarray[1]=15;
      existingarray[2]=20;

      Int[] destinationarray = new int[existingarray.Length]
      existingarray.CopyTo(destinationarray,0); 
      
      int[] destinationarray1;
      destinatioarray1=existingarray.CloneTo() as int; // exp of array.cloneto()
   }
}

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Dispose and Finalise methods

Memory management is a big challenge when you are developing a web Application/software as we know that Garbage Collector plays the main role in .Net to manage unmanaged resource and Dispose and finalize method both are part of Garbage Collector.

Dispose and finalize method both are used to reclaim the memory used by the unmanaged resource.

using System;
using System.Diagnostics;

public class A
{
   Stopwatch watch;

   public A()
   {
      watch = Stopwatch.StartNew();
      Console.WriteLine("Instantiated object");              // Instantiated object 
   } 

   public void ShowDuration()
   {
      Console.WriteLine("This instance of {0} has been in existence for {1}",this, sw.Elapsed);
   }

   ~A()
   {
      Console.WriteLine("Finalizing object");                 // Finalizing object
      sw.Stop();
      Console.WriteLine("This instance of {0} has been in existence for {1}",
                        this, sw.Elapsed);
   }
}

public class Demo
{
   public static void Main()
   {
      AClass ob = new AClass();
      ob.ShowDuration();
   }
}

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Late binding Vs Early binding

If the methods have same name and different parameter declare in a single class or methods have same name and same parameter but declare in different classes then it is called Binding or Polymorphism.

Late Binding:

It is also called runtime polymorphism; the situation arrives when methods are virtual and have same name and same parameter in different classes (must be derived class). Then it is called method overriding or late binding.

using System;  

public class Vehicle
{  
    public virtual void run()
    {  
        Console.WriteLine("Running...");  
    }  
}  

public class Bike: Vehicle  
{  
    public override void run()  
    {  
        Console.WriteLine("Bike is running safely...");  
    }      
}  

public class TestMain  
{  
    public static void Main()  
    {  
        Vehicle a= new Bike();       // object  id determined at runtime
        a.eat();  
    }  
}   


Output: Bike is running safely

Late Binding:

It is also called compile time polymorphism; the situation arrived when methods have same name but different parameter in same class.

It is also called method overloading.

using System;

public class A
{
  public void Sum(int a, int b)
  {
       Console.WriteLine(a + b);
  }

  public void Sum(int a, int b, int c)
  {
       Console.WriteLine(a + b + c);
  }
 
  static void Main(string[] args)
  {
     A ob=new A();                       // Object is determined at compile time 
     ob.Sum(5,8);
     ob.Sum(5,8,10);
  }
}

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IEnumerable & IQueryable

IEnumerable and IQueryable are used for data manipulation in LINQ from the database and collection.

using System;
using System.Collections.Generic;
using System.Reflection;
using System.Collections;
 
namespace TesIEnumerable
{
    class A
    {
        public static void Main(String[] args)
        {
            IEnumerable<int> data = from value in Enumerable.Range(1, 10) select value;
            foreach (int a in data)
            {
                Console.WriteLine(a);
            }
            
            Console.ReadLine();
        }
    }
}


Output:
1
2
3
4
5
6
7
8
9
10

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Throw Exception Vs Throw Clause

Throw Exception Example:

static
{
    try
    {
       throw new Exception(“Logical Error”);
    }
    catch(Exception ex)
    {
       console.WriteLine(“Error:” + ex.geMessage())
    }
}

Throws Clause Example:

public void method() throws ArithmeticExeption
{
  ArithmeticExeption ex = new ArithmeticException();
  throw ex;
}

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== Vs equals

The == operator compare the reference of the object while the equals compares the contents of the object see the bellow example.

namespace ConsoleApplication6
{
    class Program
    {
        static void Main(string[] args)
        {

           Object o1 = "Sachin";
           char[] c={'S','a','c','h','i','n'};
           
           Object o2 = newString(c);
           Console.WriteLine(o1==o2);            //compare the reference
           Console.WriteLine(o1.Equals(o2));     // compare the contents
          
           Console.ReadKey();

        }
    }
}

Output:
False
True

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Is Vs as operator

Is operator is used to checking the Object type and it returns the Boolean value true if the object is same otherwise returns false.

The as operator perform the conversions between compatible types.it is also work similar as Is operator but instead of return Boolean value it returns the object if they are compatible type otherwise returns null.

Example of Is Operator:

class A 
{}

class B : A
{}

public class IsOperator
{
    static void Main()
    {    
        A a = new A();
        B b = new B();

        Console.WriteLine(a is A);
        Console.WriteLine(a is Object);
        Console.WriteLine(b is A);
        Console.WriteLine(a B);
    }
}

Output:
True
True
True
False

Example of as Operator:

using System;

class A {}
class B : A {}

public class AsOperator
{
    static void Main()
    {    
        object[] objects = new object[6];
        objects[0] = new A();
        objects[1] = new B();
        objects[2] = "Hello";
        objects[3] = 12;
        objects[4] = 1.4;
        objects[5] = null;

        for (int i=0; i<objects.Length; ++i) 
        {
            string str = objects[i] as string;
            Console.Write ("{0}:", i);

            if (str != null)
                Console.WriteLine (str);
            else
                Console.WriteLine ("not a string");
        }
    }
}


Output:
0: not a string
1: not a string
2: Hello
3: not a string
4: not a string
5: not a string

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Array Vs Array List

Array Example:

namespace Example1
{
    class ArrayExample
    {
        static void display(int[] array)
        {
            Console.WriteLine("Elements of array are:");
            foreach (int i in array)
            {
                Console.Write("\t{0}", i);
            }
        }

        static void Main(string[] args)
        {
            int[] arr = new int{25,15,5,10};
            int i;
            // loop for accepting values in array
            for (i = 0; i < 4; i++)
            {
                arr[i] = Convert.ToInt32(Console.ReadLine());
            }
            ArrayExample.display(array);
            //sorting array value;
            Array.Sort(array); //use array's sort function
 
            ArrayExample.display(array);
            Console.ReadLine();
        }

    }
}

Output: Elements of array are:
5  10  15  25

ArrayList Example:

using System;
using System.Collections;

class Program
{
    static void Main()
     {
        ArrayList list = new ArrayList(); // Create an ArrayList with four strings.
        list.Add("USA");
        list.Add("London");
        list.Add("Brazil");
        list.Add("India");
       
        list.Sort();  // Sort the ArrayList.
        foreach (string value in list)
        {
            Console.WriteLine(value);
        }
        
        list.Reverse();    // Reverse the ArrayList.
        foreach (string value in list)
        { 
           Console.WriteLine(“Reverse  Arraylist…………..”)
            Console.WriteLine(value);
        }
    }
}

Output:
Brazil
India
London
USA
Reverse  Arraylist…………..
USA
London
India
Brazil

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Directcast Vs ctype

Directcast Example:

Object exp = ”public keyword is access modifier”;
String exp1 =(string) exp;
Object exp2 = exp1;
Object exp3 = (object) exp1;

Type Cast Example:

TextBox exptype=(TextBox)obj;

Where obj is  Typecast

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Public Vs Static Vs void

Public: public keyword is access modifier and tells the c# compiler that the Main method is accessible by anyone.

Static: static keyword declared that the Main method is global and can call without creating an instance of the class.

Void: void keyword is used to specify that the Main method does not return any value.

Example of public and static keyword:

using System;

namespace staticexample
{
    class A
    {
        public static int a;             // static variable can be initialised out side of member function
        public static void display()     // static and void method means no return type
        {
            a=10;
            Console.WriteLine(a);
        }
        public void demo()            //  public and void method means non return type
        {
            int b=20;
            Console.WriteLine(b);
        }

 
        static void Main(string[] args)
        {
            A obj = new A();
            A.display();              //calling display method through class name
            obj.demo();               //calling demo method using instance of class
            Console.Read();
        }
    }
}

Output: 10
        20

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Top Technical Interview Questions and Answers Series:

• Top 20 AngularJS Interview Questions
• Advanced Angular2 Interview Questions
• Top 15 Bootstrap Interview Questions
• ReactJS Interview Questions and Answers
• Top 10 HTML5 Interview Questions
• Must Have NodeJS Interview Questions
• BackboneJS Interview Questions
• Top 10 WCF Interview Questions
• Comprehensive Series of WCF Interview Questions
• Java Spring MVC Interview Questions

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