After this first chapter, the book can be divided into three parts: first, the grammar and vocabulary of the C# language; second, the types available in .NET for building app features; and third, examples of common cross-platform apps you can build using C# and .NET.

Most people learn complex topics best by imitation and repetition rather than reading a detailed explanation of the theory; therefore, I will not overload you with detailed explanations of every step throughout this book. The idea is to get you to write some code and see it run.

You don't need to know all the nitty-gritty details immediately. That will be something that comes with time as you build your own apps and go beyond what any book can teach you.

In the words of Samuel Johnson, author of the English dictionary in 1755, I have committed "a few wild blunders, and risible absurdities, from which no work of such multiplicity is free." I take sole responsibility for these and hope you appreciate the challenge of my attempt to lash the wind by writing this book about rapidly evolving technologies like C# and .NET, and the apps that you can build with them.

This first chapter covers the following topics:

• Setting up your development environment
• Understanding .NET
• Building console apps using Visual Studio 2022
• Building console apps using Visual Studio Code
• Exploring code using .NET Interactive Notebooks
• Reviewing the folders and files for projects
• Making good use of the GitHub repository for this book
• Looking for help

Setting up your development environment

• Visual Studio 2022 for Windows
• Visual Studio 2022 for Mac
• Visual Studio Code for Windows, Mac, or Linux
• GitHub Codespaces

Third parties have created their own C# code editors, for example, JetBrains Rider.

Choosing the appropriate tool and application type for learning

What is the best tool and application type for learning C# and .NET?

Having said that, you can make the argument that the best tool is the one you are already familiar with or that you or your team will use as your daily development tool. For that reason, I want you to be free to choose any C# code editor or IDE to complete the coding tasks in this book, including Visual Studio Code, Visual Studio for Windows, Visual Studio for Mac, or even JetBrains Rider.

In the third edition of this book, I gave detailed step-by-step instructions for both Visual Studio for Windows and Visual Studio Code for all coding tasks. Unfortunately, that got messy and confusing quickly. In this sixth edition, I give detailed step-by-step instructions for how to create multiple projects in both Visual Studio 2022 for Windows and Visual Studio Code only in Chapter 1. After that, I give names of projects and general instructions that work with all tools so you can use whichever tool you prefer.

The best application type for learning the C# language constructs and many of the .NET libraries is one that does not distract with unnecessary application code. For example, there is no need to create an entire Windows desktop application or a website just to learn how to write a switch statement.

For that reason, I believe the best method for learning the C# and .NET topics in Chapters 1 to 12 is to build console applications. Then, in Chapter 13 to 19 onward, you will build websites, services, and graphical desktop and mobile apps.

Pros and cons of the .NET Interactive Notebooks extension

• They cannot read input from the user, for example, you cannot use ReadLine or ReadKey.
• They cannot have arguments passed to them.
• They do not allow you to define your own namespaces.
• They do not have any debugging tools (but these are coming in the future).

Using Visual Studio Code for cross-platform development

Visual Studio Code is a good choice for modern cross-platform development because it has an extensive and growing set of extensions to support many languages beyond C#.

Being cross-platform and lightweight, it can be installed on all platforms that your apps will be deployed to for quick bug fixes and so on. Choosing Visual Studio Code means a developer can use a cross-platform code editor to develop cross-platform apps.

Visual Studio Code has strong support for web development, although it currently has weak support for mobile and desktop development.

Visual Studio Code is supported on ARM processors so that you can develop on Apple Silicon computers and Raspberry Pi.

Visual Studio Code is by far the most popular integrated development environment, with over 70% of professional developers selecting it in the Stack Overflow 2021 survey.

Using GitHub Codespaces for development in the cloud

Using Visual Studio for Mac for general development

To compile apps for Apple operating systems like iOS to run on devices like the iPhone and iPad, you must have Xcode, which only runs on macOS.

Using Visual Studio for Windows for general development

What I used

• HP Spectre (Intel) laptop
• Apple Silicon Mac mini (M1) desktop
• Raspberry Pi 400 (ARM v8) desktop

• Visual Studio Code on:
  • macOS on an Apple Silicon Mac mini (M1) desktop
  • Windows 10 on an HP Spectre (Intel) laptop
  • Ubuntu 64 on a Raspberry Pi 400
• Visual Studio 2022 for Windows on:
  • Windows 10 on an HP Spectre (Intel) laptop
• Visual Studio 2022 for Mac on:
  • macOS on an Apple Silicon Mac mini (M1) desktop

I hope that you have access to a variety of hardware and software too, because seeing the differences in platforms deepens your understanding of development challenges, although any one of the above combinations is enough to learn the fundamentals of C# and .NET and how to build practical apps and websites.

• Windows: Windows 7 SP1, or later. Windows 10 version 1607, or later, including Windows 11. Windows Server 2012 R2 SP1, or later. Nano Server version 1809, or later.
• Mac: macOS Mojave (version 10.14), or later.
• Linux: Alpine Linux 3.13, or later. CentOS 7, or later. Debian 10, or later. Fedora 32, or later. openSUSE 15, or later. Red Hat Enterprise Linux (RHEL) 7, or later. SUSE Enterprise Linux 12 SP2, or later. Ubuntu 16.04, 18.04, 20.04, or later.
• Android: API 21, or later.
• iOS: 10, or later.

Windows ARM64 support in .NET 5 and later means you can develop on, and deploy to, Windows ARM devices like Microsoft Surface Pro X. But developing on an Apple M1 Mac using Parallels and a Windows 10 ARM virtual machine is apparently twice as fast!

Downloading and installing Visual Studio 2022 for Windows

If you do not have a Windows computer, then you can skip this section and continue to the next section where you will download and install Visual Studio Code on macOS or Linux.

Microsoft Visual Studio for Windows keyboard shortcuts

Even if you plan to only use Visual Studio 2022 for Windows for development, I recommend that you download and install Visual Studio Code and try the coding tasks in this chapter using it, and then decide if you want to stick with just using Visual Studio 2022 for the rest of the book.

Let's now download and install Visual Studio Code, the .NET SDK, and the C# and .NET Interactive Notebooks extensions:

Installing other extensions

Understanding Microsoft Visual Studio Code versions

• Version 1.59, August 2021 feature release
• Version 1.59.1, August 2021 bug fix release

The version used in this book is 1.59, but the version of Microsoft Visual Studio Code is less important than the version of the C# for Visual Studio Code extension that you installed.

While the C# extension is not required, it provides IntelliSense as you type, code navigation, and debugging features, so it's something that's very handy to install and keep updated to support the latest C# language features.

Microsoft Visual Studio Code keyboard shortcuts

Since .NET Framework 4.5.2, it has been an official component of the Windows operating system. Components have the same support as their parent products, so 4.5.2 and later follow the life cycle policy of the Windows OS on which it is installed. .NET Framework is installed on over one billion computers, so it must change as little as possible. Even bug fixes can cause problems, so it is updated infrequently.

Understanding the Mono, Xamarin, and Unity projects

Understanding .NET Core

Scott Hunter, Microsoft Partner Director Program Manager for .NET, has said that "Forty percent of our .NET Core customers are brand-new developers to the platform, which is what we want with .NET Core. We want to bring new people in."

.NET Core is fast-moving, and because it can be deployed side by side with an app, it can change frequently, knowing those changes will not affect other .NET Core apps on the same machine. Most improvements that Microsoft makes to .NET Core and modern .NET cannot be easily added to .NET Framework.

Understanding the journey to one .NET

At the Microsoft Build developer conference in May 2020, the .NET team announced that their plans for the unification of .NET had been delayed. They said that .NET 5 would be released on November 10, 2020, and it would unify all the various .NET platforms except mobile. It would not be until .NET 6 in November 2021 that mobile will also be supported by the unified .NET platform.

.NET Core has been renamed .NET and the major version number has skipped the number four to avoid confusion with .NET Framework 4.x. Microsoft plans on annual major version releases every November, rather like Apple does major version number releases of iOS every September.

.NET Core 3.1 included Blazor Server for building web components. Microsoft had also planned to include Blazor WebAssembly in that release, but it was delayed. Blazor WebAssembly was later released as an optional add-on for .NET Core 3.1. I include it in the table above because it was versioned as 3.2 to exclude it from the LTS of .NET Core 3.1.

Understanding .NET support

.NET versions are either Long Term Support (LTS) or Current, as described in the following list:

To better understand your choices of Current and LTS releases, it is helpful to see it visually, with 3-year-long black bars for LTS releases, and variable-length gray bars for Current releases that end with cross-hatching for the 6 months after a new major or minor release that they retain support for, as shown in Figure 1.2:

Figure 1.2: Support for various versions

If you need long-term support from Microsoft, then choose .NET 6.0 today and stick with it until .NET 8.0, even once Microsoft releases .NET 7.0. This is because .NET 7.0 will be a current release and it will therefore lose support before .NET 6.0 does. Just remember that even with LTS releases you must upgrade to bug fix releases like 6.0.1.

All versions of .NET Core and modern .NET have reached their end of life except those shown in the following list:

• .NET 5.0 will reach end of life in May 2022.
• .NET Core 3.1 will reach end of life on December 3, 2022.
• .NET 6.0 will reach end of life in November 2024.

Understanding .NET Runtime and .NET SDK versions

You can see an example of this in the following table:

Removing old versions of .NET

You can see which SDKs and runtimes are currently installed using the following commands:

• dotnet --list-sdks
• dotnet --list-runtimes

On Windows, use the App & features section to remove .NET SDKs. On macOS or Windows, use the dotnet-core-uninstall tool. This tool is not installed by default.

For example, while writing the fourth edition, I used the following command every month:

dotnet-core-uninstall remove --all-previews-but-latest --sdk

What is different about modern .NET?

Windows development

Web development

If you have existing apps that use the old EF, then version 6.3 is supported on .NET Core 3.0 or later.

Themes of modern .NET

• .NET Core: For cross-platform and new apps
• .NET Framework: For legacy apps
• Xamarin: For mobile apps

Each had strengths and weaknesses because they were all designed for different scenarios. This led to the problem that a developer had to learn three platforms, each with annoying quirks and limitations.

Because of that, Microsoft defined .NET Standard – a specification for a set of APIs that all .NET platforms could implement to indicate what level of compatibility they have. For example, basic support is indicated by a platform being compliant with .NET Standard 1.4.

With .NET Standard 2.0 and later, Microsoft made all three platforms converge on a modern minimum standard, which made it much easier for developers to share code between any flavor of .NET.

It is important to understand that .NET Standard is just a standard. You are not able to install .NET Standard in the same way that you cannot install HTML5. To use HTML5, you must install a web browser that implements the HTML5 standard.

To use .NET Standard, you must install a .NET platform that implements the .NET Standard specification. The last .NET Standard, version 2.1, is implemented by .NET Core 3.0, Mono, and Xamarin. Some features of C# 8.0 require .NET Standard 2.1. .NET Standard 2.1 is not implemented by .NET Framework 4.8, so we should treat .NET Framework as legacy.

With the release of .NET 6 in November 2021, the need for .NET Standard has reduced significantly because there is now a single .NET for all platforms, including mobile. .NET 6 has a single BCL and two CLRs: CoreCLR is optimized for server or desktop scenarios like websites and Windows desktop apps, and the Mono runtime is optimized for mobile and web browser apps that have limited resources.

Even now, apps and websites created for .NET Framework will need to be supported, so it is important to understand that you can create .NET Standard 2.0 class libraries that are backward compatible with legacy .NET platforms.

.NET platforms and tools used by the book editions

The second edition was (almost) completely purged of all .NET Framework code examples so that readers were able to focus on .NET Core examples that truly run cross-platform.

The third edition completed the switch. It was rewritten so that all of the code was pure .NET Core. But giving step-by-step instructions for both Visual Studio Code and Visual Studio 2017 for all tasks added complexity.

The fourth edition continued the trend by only showing coding examples using Visual Studio Code for all but the last two chapters. In Chapter 20, Building Windows Desktop Apps, it used Visual Studio running on Windows 10, and in Chapter 21, Building Cross-Platform Mobile Apps, it used Visual Studio for Mac.

In the fifth edition, Chapter 20, Building Windows Desktop Apps, was moved to Appendix B to make space for a new Chapter 20, Building Web User Interfaces Using Blazor. Blazor projects can be created using Visual Studio Code.

In this sixth edition, Chapter 19, Building Mobile and Desktop Apps Using .NET MAUI, was updated to show how mobile and desktop cross-platform apps can be created using Visual Studio 2022 and .NET MAUI (Multi-platform App UI).

Understanding intermediate language

The benefit of this two-step compilation process is that Microsoft can create CLRs for Linux and macOS, as well as for Windows. The same IL code runs everywhere because of the second compilation step, which generates code for the native operating system and CPU instruction set.

Regardless of which language the source code is written in, for example, C#, Visual Basic, or F#, all .NET applications use IL code for their instructions stored in an assembly. Microsoft and others provide disassembler tools that can open an assembly and reveal this IL code, such as the ILSpy .NET Decompiler extension.

Comparing .NET technologies

Building console apps using Visual Studio 2022

If you do not have a Windows computer or you want to use Visual Studio Code, then you can skip this section since the code will be the same, just the tooling experience is different.

Managing multiple projects using Visual Studio 2022

Writing code using Visual Studio 2022

Compiling and running code using Visual Studio

The next task is to compile and run the code.

Understanding the compiler-generated folders and files

• The obj folder contains one compiled object file for each source code file. These objects haven't been linked together into a final executable yet.
• The bin folder contains the binary executable for the application or class library. We will look at this in more detail in Chapter 7, Packaging and Distributing .NET Types.

Writing top-level programs

Although the boilerplate code is written for you by the project template, is there a simpler way?

Let's compare the console app created by the project template, as shown in the following code:

using System;
namespace HelloCS
{
  class Program
  {
    static void Main(string[] args)
    {
      Console.WriteLine("Hello World!");
    }
  }
}

To the new top-level program minimum console app, as shown in the following code:

using System;
Console.WriteLine("Hello World!");

That is a lot simpler, right? If you had to start with a blank file and write all the statements yourself, this is better. But how does it work?

During compilation, all the boilerplate code to define a namespace, the Program class, and its Main method, is generated and wrapped around the statements you write.

• Any using statements still must to go at the top of the file.
• There can be only one file like this in a project.

The using System; statement at the top of the file imports the System namespace. This enables the Console.WriteLine statement to work. You will learn more about namespaces in the next chapter.

Adding a second project using Visual Studio 2022

1. In Visual Studio, navigate to File | Add | New Project.
2. In the Add a new project dialog, in Recent project templates, select Console Application [C#] and then click Next.
3. In the Configure your new project dialog, for the Project name, enter TopLevelProgram, leave the location as C:\Code\Chapter01, and then click Next.
4. In the Additional information dialog, select .NET 6.0 (Long-term support), and then click Create.
5. In Solution Explorer, in the TopLevelProgram project, double-click Program.cs to open it.
6. In Program.cs, note the code consists of only a comment and a single statement because it uses the top-level program feature introduced in C# 9, as shown in the following code:

   // See https://aka.ms/new-console-template for more information
   Console.WriteLine("Hello, World!");
   

But when I introduced the concept of top-level programs earlier, we needed a using System; statement. Why don't we need that here?

Implicitly imported namespaces

Building console apps using Visual Studio Code

The goal of this section is to showcase how to build a console app using Visual Studio Code.

The main differences will be native command-line actions such as deleting a file: both the command and the path are likely to be different on Windows or macOS and Linux. Luckily, the dotnet command-line tool will be identical on all platforms.

Managing multiple projects using Visual Studio Code

Writing code using Visual Studio Code

Compiling and running code using the dotnet CLI

Figure 1.11: The output of running your first console application

Adding a second project using Visual Studio Code

If you were to run the program on macOS Big Sur, the environment operating system would be different, as shown in the following output:

Hello from a Top Level Program!
Unix 11.2.3

Managing multiple files using Visual Studio Code

If you have multiple files that you want to work with at the same time, then you can put them side by side as you edit them:

1. In EXPLORER, expand the two projects.
2. Open both Program.cs files from the two projects.
3. Click, hold, and drag the edit window tab for one of your open files to arrange them so that you can see both files at the same time.

Exploring code using .NET Interactive Notebooks

Creating a notebook

Writing and running code in a notebook

Next, we can write code in the notebook cells:

Saving a notebook

Adding Markdown and special commands to a notebook

Executing code in multiple cells

Using .NET Interactive Notebooks for the code in this book

The result is a folder structure and files that will be repeated in subsequent chapters, although with more than just two projects, as shown in Figure 1.18:

Figure 1.18: Folder structure and files for the two projects in this chapter

Understanding the common folders and files

• In Visual Studio 2022, with a solution open, navigate to File | Add Existing Project… to add a project file created by another tool.
• In Visual Studio Code, with a workspace open, navigate to File | Add Folder to Workspace… to add a project folder created by another tool.

  Good Practice: Although the source code, like the .csproj and .cs files, is identical, the bin and obj folders that are automatically generated by the compiler could have mismatched file versions that give errors. If you want to open the same project in both Visual Studio 2022 and Visual Studio Code, delete the temporary bin and obj folders before opening the project in the other code editor. This is why I asked you to create a different folder for the Visual Studio Code solutions in this chapter.

Understanding the solution code on GitHub

• To store the solution code for the book that can be maintained after the print publication date.
• To provide extra materials that extend the book, like errata fixes, small improvements, lists of useful links, and longer articles that cannot fit in the printed book.
• To provide a place for readers to get in touch with me if they have issues with the book.

Raising issues with the book

Giving me feedback

I love to hear from my readers about what they like about my book, as well as suggestions for improvements and how they are working with C# and .NET, so don't be shy. Please get in touch!

Thank you in advance for your thoughtful and constructive feedback.

Downloading solution code from the GitHub repository

Using Git with Visual Studio Code and the command line

Looking for help

This section is all about how to find quality information about programming on the web.

Reading Microsoft documentation

Getting definitions of types and their members

One of the most useful features of a code editor is Go To Definition. It is available in Visual Studio Code and Visual Studio 2022. It will show what the public definition of the type or member looks like by reading the metadata in the compiled assembly.

Some tools, such as ILSpy .NET Decompiler, will even reverse-engineer from the metadata and IL code back into C# for you.

• A summary that describes the method.
• Parameters like the string value that can be passed to the method.
• The return value of the method, including its data type.
• Three exceptions that might occur if you call this method, including ArgumentNullException, FormatException, and OverflowException. Now, we know that we could choose to wrap a call to this method in a try statement and which exceptions to catch.

Hopefully, you are getting impatient to learn what all this means!

Be patient for a little longer. You are almost at the end of this chapter, and in the next chapter, you will dive into the details of the C# language. But first, let's see where else you can look for help.

Looking for answers on Stack Overflow

1. Navigate to Google.
2. Search for information about garbage collection using a simple Google query, and note that you will probably see a lot of ads for garbage collection services in your local area before you see the Wikipedia definition of garbage collection in computer science.
3. Improve the search by restricting it to a useful site such as Stack Overflow, and by removing languages that we might not care about, such as C++, Rust, and Python, or by adding C# and .NET explicitly, as shown in the following search query:

   garbage collection site:stackoverflow.com +C# -Java
   

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