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Null Value

Explore how null values represent missing data in C#, distinguish between reference and value types, and learn to use nullable types with the ? syntax. Understand the importance of null checks and the null coalescing operator ?? to write safer and more robust code that prevents NullReferenceException errors.

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The null and reference types

In C#, we have a special value called null. This value represents the absence of value and is the default for reference-type variables.

string name = null;

The null value means that a variable doesn’t point to anything in memory. Because we’re dealing with references, we can’t assign null to a value-type variable, such as int.

If we try to access a variable that doesn’t point to anything, we get a NullReferenceException:

C#
using System;
namespace NullValue
{
    class Program
    {
        static void Main(string[] args)
        {
            string name = null;
            // name is null. Accessing its members and methods
            // will yield an error
            string nameInUpperCase = name.ToUpper();
            Console.WriteLine(nameInUpperCase);
        }
    }
}

The null and value types

Unlike reference types, value-type variables can’t be assigned the null value directly. However, it’s quite common to potentially need a value-type to be null. For instance, if we’re fetching ...