using System;

public class Program

{

    public static void Main()

    {

        TestClass tc = null;

        //TestClass tc = new TestClass() { A = 5 };

        if (tc?.A == null) {

            Console.WriteLine("value is null"); 

        }

        if (null != 0)

        {

            Console.WriteLine("zero doesn't equal null");   

        }

        if (tc?.A != 0)

        {

            Console.WriteLine("value is null and doesn't equal zero");  

        }

        if ((tc?.A ?? 0) != 0)

        {

            Console.WriteLine("not zero or null");

        }

    }

}

​

public class TestClass

{

    public int A {get;set;}

}