C# Tutorial P6 - Nullable Types

[Admin]

In C# types are divided into 2 broad categories.
Value Types - int, float, double, structs, enums etc
Reference Types – Interface, Class, delegates, arrays etc

By default value types are non nullable. To make them nullable use ?
int i = 0 (i is non nullable, so "i" cannot be set to null, i = null will generate compiler error)
int? j = 0 (j is nullable int, so j=null is legal)

Nullable types bridge the differences between C# types and Database types

Samples Code:

using System;

class Program
{
    static void Main()
    {
        // string Name = null;
        // int? i = null;
        // bool? AreYouMajor = null;

        if (AreYouMajor == true)
        {
            Console.WriteLine("User is Major");
        }
        else if (!AreYouMajor.Value)    // else if (AreYouMajor == false)
        {
            Console.WriteLine("User is not Major");
        }
        else
        {
            Console.WriteLine("User did not answer the question");
        }      
    }
}

Program without using NULL coalescing operator
using System;
class Program
{
    static void Main()
    {
        int AvailableTickets;
        int? TicketsOnSale = null;

        if (TicketsOnSale == null)
        {
            AvailableTickets = 0;
        }
        else
        {
            AvailableTickets = (int)TicketsOnSale;   // AvailableTickets = TicketsOnSale.Value;
        }

        Console.WriteLine("Available Tickets={0}", AvailableTickets);
    }
}

The above program is re-written using NULL coalescing operator
using System;
class Program
{
    static void Main()
    {
        int AvailableTickets;
        int? TicketsOnSale = null;

        //Using null coalesce operator ??
        AvailableTickets = TicketsOnSale ?? 0;

        Console.WriteLine("Available Tickets={0}", AvailableTickets);
    }
}