Declaration of nullable variable:

int ?a =null;//a is the nullable variable here and ? is the nullable variable operator.

Null Colecasing Operator: - With the help of null coleascing operator we assign a value into null variable if it will have a null value in it then it will assign a different variable value otherwise the default value will be assigned.

Declaration of Null Colecasing Operator :

int b = 45;

int? c = null;

int d = c ?? b;

Sample Code :

using System;
using System.Collections.Generic;
using System.Text;
  
namespace ConsoleApplication1
{
    classProgram
    {
        staticvoid Main(string[] args)
         {
            int ?a =null;// This is how we can implement a null value in the integer type variable by using nullable type variable
            int b = 45;
            a = b;
            if (a.HasValue)
            {
                Console.WriteLine("The value of a is : " + a);
            }
            int? c = null;
            int d = c ?? b;
            
            /*
             *  This is the implementation of null coleacsing operator
             *  A null coleascing operator cxhecks that a variable has a null value or not if it will
             *  have a null Value then it will put the default variable value of varible [b]
              */
            Console.WriteLine("The value of d : " + d);
         }
    }
}