using System;
 
namespace Nullable
{
    class MainApp
    {
        static void Main(string[] args)
        {
            int? a = null;
 
            Console.WriteLine(a.HasValue);
            Console.WriteLine(a==null);
 
            a = 3;
            Console.WriteLine(a.HasValue);
            Console.WriteLine(a!= null);
            Console.WriteLine(a.Value);
 
        }
    }
}