Introducing C#

This part of the book is about the C# language—the grammar and vocabulary that you will use every day to write the source code for your applications.

Programming languages have many similarities to human languages, except that in programming languages, you can make up your own words, just like Dr. Seuss!

In a book written by Dr. Seuss in 1950, If I Ran the Zoo, he states this:

"And then, just to show them, I'll sail to Ka-Troo And Bring Back an It-Kutch, a Preep, and a Proo, A Nerkle, a Nerd, and a Seersucker, too!"

Understanding language versions and features

This part of the book covers the C# programming language and is written primarily for beginners, so it covers the fundamental topics that all developers need to know, from declaring variables to storing data to how to define your own custom data types.

Advanced and obscure topics like ref local variable reassignment and reference semantics with value types are not covered.

This book covers features of the C# language from version 1.0 up to the latest version, 9.0. If you already have some familiarity with older versions of C# and are excited to find out about the new features in the most recent versions of C#, I have made it easier for you to jump around by listing language versions and their important new features below, along with the chapter number and topic title where you can learn about them.

C# 1.0

C# 1.0 was released in 2002 and included all the important features of a statically typed object-oriented modern language, as you will see throughout chapters 2 to 6.

C# 2.0

C# 2.0 was released in 2005 and focused on enabling strong data typing using generics, to improve code performance and reduce type errors, including the topics listed in the following table:

C# 3.0

C# 3.0 was released in 2007 and focused on enabling declarative coding with Language INtegrated Queries (LINQ) and related features like anonymous types and lambda expressions, including the topics listed in the following table:

C# 4.0

C# 4.0 was released in 2010 and focused on improving interoperability with dynamic languages like F# and Python, including the topics listed in the following table:

C# 5.0

C# 5.0 was released in 2012 and focused on simplifying asynchronous operation support by automatically implementing complex state machines while writing what looks like synchronous statements, including the topics listed in the following table:

C# 6.0

C# 6.0 was released in 2015 and focused on minor refinements to the language, including the topics listed in the following table:

C# 7.0

C# 7.0 was released in March 2017 and focused on adding functional language features like tuples and pattern matching, as well as minor refinements to the language, including the topics listed in the following table:

C# 7.1

C# 7.1 was released in August 2017 and focused on minor refinements to the language, including the topics listed in the following table:

C# 7.2

C# 7.2 was released in November 2017 and focused on minor refinements to the language, including the topics listed in the following table:

C# 7.3

C# 7.3 was released in May 2018 and focused on performance-oriented safe code that improves ref variables, pointers, and stackalloc. These are advanced and rarely needed for most developers, so they are not covered in this book.

C# 8.0

C# 8.0 was released in September 2019 and focused on a major change to the language related to null handling, including the topics listed in the following table:

C# 9.0

C# 9.0 was released in November 2020 and focused on record types, refinements to pattern matching, and minimal-code console apps, including the topics listed in the following table:

Discovering your C# compiler versions

With the C# 7.x generation, Microsoft decided to increase the cadence of language releases, releasing minor version numbers, also known as point releases, for the first time since C# 1.1.

.NET language compilers for C# and Visual Basic, also known as Roslyn, along with a separate compiler for F#, are distributed as part of .NET SDK. To use a specific version of C#, you must have at least that version of .NET SDK installed, as shown in the following table:

Let's see what .NET SDK and C# language compiler versions you have available:

1. Start Visual Studio Code.
2. Navigate to View | Terminal.
3. To determine which version of the .NET SDK you have available, enter the following command:

   dotnet --version
   

4. Note the version at the time of writing is 5.0.100, indicating that it is the initial version of the SDK without any bug fixes or new features yet, as shown in the following output:

   5.0.100
   

5. To determine which versions of the C# compiler you have available, enter the following command:

   csc -langversion:?
   

6. Note all the versions available at the time of writing, as shown in the following output:

   Supported language versions:
   default
   1
   2
   3
   4
   5
   6
   7.0
   7.1
   7.2
   7.3
   8.0
   9.0 (default)
   latestmajor
   preview
   latest
   

Enabling a specific language version compiler

Developer tools like Visual Studio Code and the dotnet command-line interface assume that you want to use the latest major version of a C# language compiler by default. Before C# 8.0 was released, C# 7.0 was the latest major version and was used by default. To use the improvements in a C# point release like 7.1, 7.2, or 7.3, you had to add a configuration element to the project file, as shown in the following markup:

<LangVersion>7.3</LangVersion>

After the release of C# 9.0 with .NET 5.0, if Microsoft releases a C# 9.1 compiler and you want to use its new language features then you will have to add a configuration element to your project file, as shown in the following markup:

<LangVersion>9.1</LangVersion>

Potential values for the <LangVersion> are shown in the following table:

After creating a new project with the dotnet command-line tool, you can edit the csproj file and add the <LangVersion> element, as shown highlighted in the following markup:

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net5.0</TargetFramework>
    <LangVersion>preview</LangVersion>
  </PropertyGroup>
</Project>

Your projects must target net5.0 to use the full features of C# 9.

If you have not done so already, install the extension MSBuild project tools. This will give you IntelliSense while editing .csproj files, including making it easy to add the <LangVersion> element with appropriate values.