Nullable Types in C#: Handling Missing or Undefined Values

Understand and utilize nullable types in C# for robustly handling situations where values might be missing or undefined. This tutorial explains declaring nullable types using both syntaxes (`Nullable` and `T?`), demonstrates checking for null values, and highlights their importance in working with potentially incomplete data from various sources.

Nullable Types in C#

In C#, nullable types allow a variable to hold either a value of its declared type or a `null` value. This is particularly useful when dealing with data that might be missing or undefined, such as data coming from a database or a web service where a field may not always have a value assigned to it.

Creating Nullable Types

There are two ways to declare a nullable type in C#:

1. Using the `System.Nullable` struct: `Nullable myNullableInt;`
2. Using the `?` operator: `int? myNullableInt;` (shorthand notation)

Note: You cannot make reference types (like classes) nullable. Only value types (like `int`, `float`, `bool`, etc.) can be nullable.

Example 1: Using `System.Nullable`

using System;

public class NullableExample {
    public static void Main(string[] args) {
        Nullable<int> a = 10;  // a is nullable int
        Console.WriteLine(a.Value); // Accesses the value (throws exception if null)

        a = null;
        if (a.HasValue) { 
            Console.WriteLine(a.Value); 
        } else {
            Console.WriteLine("a is null.");
        }
    }
}

Example 2: Using the `?` Operator

This example demonstrates the shorthand syntax for creating nullable types using the `?` operator:

int? x = 10; // x is a nullable int
double? y = null; // y is a nullable double
bool? z = true; // z is a nullable boolean

Checking for Null Values

Use the `HasValue` property to check if a nullable type variable has a value or is null:

if (myNullableInt.HasValue) {
    int value = myNullableInt.Value; // Access the value if it's not null
}