C# - null coalescing operator (??)

The null coalescing operator in C# is represented by ??. It is used to provide a default value for nullable value types and reference types, helping to avoid null reference exceptions in your code.

Here's a simple example to illustrate how the null coalescing operator works:

using System;

class NullCoalescingExample
{
static void Main()
{
	// Nullable int with a value
	int? numberWithAValue = 10;
	// Nullable int without a value (null)
	int? nullNumber = null;

	// Using the null coalescing operator
	int result1 = numberWithAValue ?? 0;
	int result2 = nullNumber ?? -1;

	// Displaying results
	Console.WriteLine("Result 1 (non-null value): " + result1); // Outputs 10
	Console.WriteLine("Result 2 (null value): " + result2); // Outputs -1
}
}
 

In this code:

• We have two nullable integers (int?). One is assigned a value (10), and the other is null.
• We then use the null coalescing operator to set result1 and result2. If the nullable integer has a value, that value is used. If it is null, the operator returns the value provided after ??.
• So, result1 becomes 10 (as numberWithAValue has a value), and result2 becomes -1 (as nullNumber is null).

The output of this program will be:

	Result 1 (non-null value): 10
	Result 2 (null value): -1
 

This example demonstrates how the null coalescing operator can simplify handling null values and provide default values when needed.

Points to Remember:

1. Purpose: The null coalescing operator (`??`) is used to handle situations where a value might be null, and we want to provide a default value if it is indeed null.
2. Nullable Values: It works with both nullable value types (like `int?`, `double?`) and reference types (like strings).
3. Syntax: The operator consists of two question marks (`??`) placed between the nullable value and the default value.
4. Checking for Null: It checks if the left-side value is null. If it's not null, it returns that value. If it is null, it returns the right-side default value.
5. Avoiding Null Reference Exceptions: It's a handy tool to prevent null reference exceptions, which can crash your program when you try to access properties or methods on null objects.
6. Default Values: You can set any value as the default, whether it's a number, string, or even another variable.
7. Use Cases: Common use cases include providing default values for user inputs, database queries, or configuration settings.
8. Simplified Code: It simplifies code by reducing the need for explicit null checks and conditional statements.
9. Example: In `int? number = null; int result = number ?? 5;`, if `number` is null, `result` will be set to `5`.
10. Chaining: You can chain multiple null coalescing operators together to handle nested null values.