EN CSharp Keyword null

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C#: null

Handbook C# · Practical Guide

Missing reference or nullable value. Not an empty string or number 0.

Simple example (Example.cs)

Save this example separately as Example.cs. Run it independently of the other examples on this page.

Example.cs:

// PROJECT-EXAMPLE
string? name = null;
System.Console.WriteLine(name ?? "Unknown");

Result:

Unknown

Syntax

string? text = null;

Example 1: simple form

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using System.IO;
using System.Runtime.InteropServices;
using System.Runtime.CompilerServices;

public static class Program
{
    public static async Task Main(string[] args)
    {
        string? name = null;
        Console.WriteLine(name ?? "Unknown");
    }
}

Example 2: another practical form

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using System.IO;
using System.Runtime.InteropServices;
using System.Runtime.CompilerServices;

public static class Program
{
    public static async Task Main(string[] args)
    {
        int? amount = null;
        Console.WriteLine(amount.HasValue);
        amount = 5;
        Console.WriteLine(amount.GetValueOrDefault());
    }
}

Official source: Microsoft Learn.