Understanding Is and As operator

This example states the purpose of the "is" and "as" operator during casting.  

Both is and as operators are used to check the type of object referred by object reference and also type caste if possible. 

Operator is can be used to test whether an object reference refers to an object of the given type. 

Operator as can be used to type cast one type to another provided the expression is compatible with the given type. If not compatible than null is assigned to the object reference. 

like in example below 

c2 = rd2 as ResidentalDoctors1;  here c2 is assigned null because rd2 is consultant reference type and c2 is referring to resident type.

 using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

namespace Apps

{

    class Doctor1

    {

        protected string name, specialization;

        public Doctor1(string name, string specialization)

        {

            this.name = name;

            this.specialization = specialization;

        }

        public void Print()

        {

            Console.WriteLine(name);

            Console.WriteLine(specialization);

        }

    }

    class ResidentalDoctors1 : Doctor1

    {

        protected int salary;

        public ResidentalDoctors1(string name, string specialization, int salary)

            : base(name, specialization)

        {

            this.salary = salary;

        }

        public new void Print()

        {

            base.Print();

            Console.WriteLine(salary);

        }

        public int GetPay()

        {

            return salary;

        }

    }

    class Consultant1 : Doctor1

    {

        protected int fees, visitNum;

        public Consultant1(string name, string specialization, int fees, int visitNum)

            : base(name, specialization)

        {

            this.fees = fees;

            this.visitNum = visitNum;

        }

        public new void Print()

        {

            base.Print();

            Console.WriteLine(fees);

            Console.WriteLine(visitNum);

        }

        public int GetPay()

        {

            return fees * visitNum;

        }

    }

 class UnderstandingISandASoperator

 {

 public static void Main()

{

 //The below three lines of code will lead to exception i.e known at runtime. Since d reference is pointing to consultant, but it is assigned to c (ResidentalDoctors1 object)

Doctor1 d = new Consultant1("Chitti", "General", 300, 10);  // Upcasting

ResidentalDoctors1 c;

c = (ResidentalDoctors1)d;  // Downcasting leads to exception. Not safe way to do this casting.

//  To overcome above problem we will see 2 ways to resolve this

 // 1. Example

Doctor1 rd = new Consultant1("Steve", "General", 100, 100);

ResidentalDoctors1 c;

 if (rd is ResidentalDoctors1)       // using is operator we are handling to avoid exception.

{

 // Below statements are executed only if rd is object reference to ResidentalDoctors1

c = (ResidentalDoctors1)rd;  // Downcasting leads to exception

Console.WriteLine("rd is a object reference to ResidentalDoctors1 class");

}

//  2. Example

Doctor1 rd2 = new Consultant1("Steve", "General", 100, 100);

ResidentalDoctors1 c2;

c2 = rd2 as ResidentalDoctors1; 

 // Here there is no condition and to check unlike is operator but as operator will handle exception internally and assigns null to it if thrown.

Console.WriteLine(c2);

 // This example below will complete the casting as c3 is referring to Consultant1 and rd3 is downcasted to Consultant1.

Doctor1 cd3 = new Consultant1("Steve", "General", 100, 100);

Consultant1 c3;

c3 = cd3 as Consultant1;

Console.WriteLine(c3);

        }

    }

}