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.

This book covers features of the C# language from version 1 up to the latest version, 11.

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.

Project COOL

Before the first release of C#, it had the codename COOL (C-like Object-Oriented Language).

C# 1

C# 1 was released in February 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# 1.2

C# 1.2, with a few minor improvements like automatic disposal at the end of foreach statements, was released with Visual Studio .NET 2003.

C# 2

C# 2 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

C# 3 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

C# 4 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

C# 5 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

C# 6 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

C# 8 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

C# 9 was released in November 2020 and focused on record types, refinements to pattern matching, and minimal-code projects, including the topics listed in the following table:

C# 10

C# 10 was released in November 2021 and focused on features that minimize the amount of code needed in common scenarios, including the topics listed in the following table:

C# 11

C# 11 was released in November 2022 and focused on features that simplify your code, including the topics listed in the following table:

Understanding C# standards

Over the years, Microsoft has submitted a few versions of C# to standards bodies, as shown in the following table:

More practically useful than the ECMA standards are the public GitHub repositories for making the work on C# and related technologies as open as possible, as shown in the following table:

Discovering your C# compiler versions

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

When you create class libraries, you can choose to target .NET Standard as well as versions of modern .NET. They have default C# language versions, as shown in the following table:

How to output the SDK version

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

1. On Windows, start Windows Terminal or Command Prompt. On macOS, start Terminal.
2. To determine which version of the .NET SDK you have available, enter the following command:

   dotnet --version
   

3. Note that the version at the time of publishing is 7.0.100, indicating that it is the initial version of the SDK without any bug fixes or new features yet, as shown in the following output:

   7.0.100
   

Enabling a specific language version compiler

Developer tools like Visual Studio 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 <LangVersion> configuration element to the project file, as shown in the following markup:

<LangVersion>7.3</LangVersion>

After the release of C# 11 with .NET 7, if Microsoft releases a C# 11.1 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>11.1</LangVersion>

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

After creating a new project, 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>net7.0</TargetFramework>
    <LangVersion>preview</LangVersion>
  </PropertyGroup>
</Project>

Switching the C# compiler for .NET 6

.NET 6 is an LTS release, so Microsoft must support developers who continue to use .NET 6 for six months longer than .NET 7. With .NET SDK 6.0.200 and later, which was released in February 2022, you can set the language version to preview to start exploring C# 11 language features. I expect that whatever version is released alongside .NET SDK 7.0.100 on November 8, 2022 (probably .NET SDK 6.0.500), it will default to using the C# 10 compiler unless you explicitly set the language version to 11, as shown highlighted in the following markup:

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net6.0</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
    <LangVersion>11</LangVersion>
  </PropertyGroup>
</Project>

If you target net7.0, which your projects will do by default if you have installed the .NET 7 SDK, then the default language will be C# 11 so it does not need to be explicitly set.

To learn simple C# language features, you can use Polyglot Notebooks, which remove the need to create an application of any kind.

To learn some other C# language features, you will need to create an application. The simplest type of application is a console app.

Let’s start by looking at the basics of the grammar and vocabulary of C#. Throughout this chapter, you will create multiple console apps, with each one showing related features of the C# language.

Showing the compiler version

We will start by writing code that shows the compiler version:

1. If you’ve completed Chapter 1, Hello, C#! Welcome, .NET!, then you will already have a cs11dotnet7 folder. If not, then you’ll need to create it.
2. Use your preferred code editor to create a new project, as defined in the following list:
   • Project template: Console App [C#]/console
   • Project file and folder: Vocabulary
   • Workspace/solution file and folder: Chapter02

   Good Practice: If you have forgotten how, or did not complete the previous chapter, then step-by-step instructions for creating a workspace/solution with multiple projects are given in Chapter 1, Hello, C#! Welcome, .NET!.

3. Open the Program.cs file, and under the comment, add a statement to show the C# version as an error, as shown in the following code:

   #error version
   

4. Run the console app:
   • If you are using Visual Studio Code, then in a terminal, enter the command dotnet run.
   • If you are using Visual Studio 2022, then navigate to Debug | Start Without Debugging. When prompted to continue and run the last successful build, click No.
5. Note that the compiler version and the language version appear as a compiler error message number CS8304, as shown in Figure 2.1:

Figure 2.1: A compiler error that shows the C# language version

6. The error message in the Visual Studio Code PROBLEMS window or Visual Studio Error List window says Compiler version: ‘4.4.0...’ with language version default (11.0).
7. Comment out the statement that causes the error, as shown in the following code:

   // #error version
   

8. Note that the compiler error messages disappear.

Understanding C# grammar

The grammar of C# includes statements and blocks. To document your code, you can use comments.

Statements

In English, we indicate the end of a sentence with a full stop. A sentence can be composed of multiple words and phrases, with the order of words being part of the grammar. For example, in English, we say “the black cat.”

The adjective, black, comes before the noun, cat. Whereas French grammar has a different order; the adjective comes after the noun: “le chat noir.” What’s important to take away from this is that the order matters.

C# indicates the end of a statement with a semicolon. A statement can be composed of multiple variables and expressions. For example, in the following statement, totalPrice is a variable and subtotal + salesTax is an expression:

var totalPrice = subtotal + salesTax;

The expression is made up of an operand named subtotal, an operator +, and another operand named salesTax. The order of operands and operators matters.

Comments

Comments are the primary method of documenting your code to increase understanding of how it works, for other developers to read, or even yourself when you come back to it months later.

You can add comments to explain your code using a double slash, //. The compiler will ignore everything after the // until the end of the line, as shown in the following code:

// sales tax must be added to the subtotal
var totalPrice = subtotal + salesTax;

To write a multiline comment, use /* at the beginning and */ at the end of the comment, as shown in the following code:

/*
This is a 
multi-line comment.
*/

Although /* */ is most commonly used for multiline comments, it is also useful for commenting in the middle of a statement, as shown in the following code:

var totalPrice = subtotal /* for this item */ + salesTax;

Your code editor has commands to make it easier to add and remove comment characters, as shown in the following list:

• Visual Studio 2022 for Windows: Navigate to Edit | Advanced | Comment Selection or Uncomment Selection.
• Visual Studio Code: Navigate to Edit | Toggle Line Comment or Toggle Block Comment.

Blocks

In English, we indicate a new paragraph by starting a new line. C# indicates a block of code with the use of curly brackets, { }.

Blocks start with a declaration to indicate what is being defined. For example, a block can define the start and end of many language constructs including namespaces, classes, methods, or statements like foreach.

You will learn more about namespaces, classes, and methods later in this chapter and subsequent chapters, but to briefly introduce some of those concepts now:

• A namespace contains types like classes to group them together.
• A class contains the members of an object, including methods.
• A method contains statements that implement an action that an object can take.

Examples of statements and blocks

In a simple console app that does not use the top-level program feature, I’ve added some comments to the statements and blocks, as shown in the following code:

using System; // a semicolon indicates the end of a statement
namespace Basics
{ // an open brace indicates the start of a block
  class Program
  {
    static void Main(string[] args)
    {
      Console.WriteLine("Hello World!"); // a statement
    }
  }
} // a close brace indicates the end of a block

Understanding C# vocabulary

The C# vocabulary is made up of keywords, symbol characters, and types.

Some of the predefined, reserved keywords that you will see in this book include using, namespace, class, static, int, string, double, bool, if, switch, break, while, do, for, foreach, and, or, not, record, and init.

Some of the symbol characters that you will see include ", ', +, -, *, /, %, @, and $.

There are other contextual keywords that only have a special meaning in a specific context.

However, that still means that there are only about 100 actual C# keywords in the language.

Warning CS8981 The type name 'person' only contains lower-cased ascii characters. Such names may become reserved for the language.

Comparing programming languages to human languages

The English language has more than 250,000 distinct words, so how does C# get away with only having about 100 keywords? Moreover, why is C# so difficult to learn if it has only 0.0416% of the number of words in the English language?

One of the key differences between a human language and a programming language is that developers need to be able to define the new “words” with new meanings. Apart from the (about) 100 keywords in the C# language, this book will teach you about some of the hundreds of thousands of “words” that other developers have defined, but you will also learn how to define your own “words.”

Programmers all over the world must learn English because most programming languages use English words such as “namespace” and “class.” There are programming languages that use other human languages, such as Arabic, but they are rare. If you are interested in learning more, this YouTube video shows a demonstration of an Arabic programming language: https://youtu.be/dkO8cdwf6v8.

Changing the color scheme for C# syntax

By default, Visual Studio 2022 and Visual Studio Code show C# keywords in blue to make them easier to differentiate from other code. Both tools allow you to customize the color scheme.

In Visual Studio 2022:

1. Navigate to Tools | Options.
2. In the Options dialog box, in the Environment section, select Fonts and Colors, and then select the display items that you would like to customize. You can also search for the section instead of browsing for it.

In Visual Studio Code:

1. Navigate to File | Preferences | Color Theme. It is in the Code menu on macOS.
2. Select a color theme. For reference, I’ll use the Light+ (default light) color theme so that the screenshots look better in a printed book.

Help for writing correct code

Plain text editors such as Notepad don’t help you write correct English. Likewise, Notepad won’t help you write correct C# either.

Microsoft Word can help you write English by highlighting spelling mistakes with red squiggles, with Word saying that “icecream” should be ice-cream or ice cream, and grammatical errors with blue squiggles, such as a sentence should have an uppercase first letter.

Similarly, Visual Studio 2022 and Visual Studio Code’s C# extension help you write C# code by highlighting spelling mistakes, such as the method name should be WriteLine with an uppercase L, and grammatical errors, such as statements that must end with a semicolon.

The C# extension constantly watches what you type and gives you feedback by highlighting problems with colored squiggly lines, like that of Microsoft Word.

Let’s see it in action:

1. In Program.cs, change the L in the WriteLine method to lowercase.
2. Delete the semicolon at the end of the statement.
3. In Visual Studio Code, navigate to View | Problems, or in Visual Studio, navigate to View | Error List, and note that a red squiggle appears under the code mistakes and details are shown, as you can see in Figure 2.2:

Figure 2.2: The Error List window showing two compile errors

4. Fix the two coding errors.

Importing namespaces

System is a namespace, which is like an address for a type. To refer to someone’s location exactly, you might use Oxford.HighStreet.BobSmith, which tells us to look for a person named Bob Smith on the High Street in the city of Oxford.

System.Console.WriteLine tells the compiler to look for a method named WriteLine in a type named Console in a namespace named System.

To simplify our code, the Console App project template for every version of .NET before 6.0 added a statement at the top of the code file to tell the compiler to always look in the System namespace for types that haven’t been prefixed with their namespace, as shown in the following code:

using System; // import the System namespace

We call this importing the namespace. The effect of importing a namespace is that all available types in that namespace will be available to your program without needing to enter the namespace prefix, and will be seen in IntelliSense while you write code.

Polyglot Notebooks have most namespaces imported automatically.

Implicitly and globally importing namespaces

Traditionally, every .cs file that needs to import namespaces would have to start with using statements to import those namespaces. Namespaces like System and System.Linq are needed in almost all .cs files, so the first few lines of every .cs file often had at least a few using statements, as shown in the following code:

using System;
using System.Linq;
using System.Collections.Generic;

When creating websites and services using ASP.NET Core, there are often dozens of namespaces that each file would have to import.

C# 10 introduced a new keyword combination and .NET SDK 6 introduced a new project setting that work together to simplify importing common namespaces.

The global using keyword combination means you only need to import a namespace in one .cs file and it will be available throughout all .cs files. You could put global using statements in the Program.cs file, but I recommend creating a separate file for those statements named something like GlobalUsings.cs with the contents being all your global using statements, as shown in the following code:

global using System;
global using System.Linq;
global using System.Collections.Generic;

Any projects that target .NET 6.0 or later, and therefore use the C# 10 or later compiler, generate a <ProjectName>.GlobalUsings.g.cs file in the obj\Debug\net7.0 folder to implicitly globally import some common namespaces like System. The specific list of implicitly imported namespaces depends on which SDK you target, as shown in the following table:

Let’s see the current autogenerated implicit imports file:

1. If you are using Visual Studio 2022, then in Solution Explorer, select the Vocabulary project, toggle on the Show All Files button, and note the compiler-generated bin and obj folders are now visible.
2. Expand the obj folder, expand the Debug folder, expand the net7.0 folder, and open the file named Vocabulary.GlobalUsings.g.cs.

   The naming convention for this file is <ProjectName>.GlobalUsings.g.cs. Note the g for generated to differentiate from developer-written code files.

3. Remember that this file is automatically created by the compiler for projects that target .NET 6.0, and that it imports some commonly used namespaces, including System.Threading, as shown in the following code:

   // <autogenerated />
   global using global::System;
   global using global::System.Collections.Generic;
   global using global::System.IO;
   global using global::System.Linq;
   global using global::System.Net.Http;
   global using global::System.Threading;
   global using global::System.Threading.Tasks;
   

4. Close the Vocabulary.GlobalUsings.g.cs file.
5. In Solution Explorer, select the project, and then add additional entries to the project file to control which namespaces are implicitly imported, as shown highlighted in the following markup:

   <Project Sdk="Microsoft.NET.Sdk">
     <PropertyGroup>
       <OutputType>Exe</OutputType>
       <TargetFramework>net7.0</TargetFramework>
       <Nullable>enable</Nullable>
       <ImplicitUsings>enable</ImplicitUsings>
     </PropertyGroup>
     <ItemGroup>
       <Using Remove="System.Threading" />
       <Using Include="System.Numerics" />
     </ItemGroup>
   </Project>
   

   Note that <ItemGroup> is different from <ImportGroup>. Be sure to use the correct one! Also note that the order of elements in a project group or item group does not matter. For example, <Nullable> can be before or after <ImplicitUsings>.

6. Save the changes to the project file.
7. Expand the obj folder, expand the Debug folder, expand the net7.0 folder, and open the file named Vocabulary.GlobalUsings.g.cs.
8. Note this file now imports System.Numerics instead of System.Threading, as shown highlighted in the following code:

   // <autogenerated />
   global using global::System;
   global using global::System.Collections.Generic;
   global using global::System.IO;
   global using global::System.Linq;
   global using global::System.Net.Http;
   global using global::System.Numerics;
   global using global::System.Threading.Tasks;
   

9. Close the Vocabulary.GlobalUsings.g.cs file.

You can disable the implicitly imported namespaces feature for all SDKs by removing the <ImplicitUsings> element completely from the project file, or changing its value to disable, as shown in the following markup:

<ImplicitUsings>disable</ImplicitUsings>

If you are using Visual Studio 2022, then you can control project settings in the user interface:

1. In Solution Explorer, right-click the Vocabulary project and select Properties.
2. Click Build and note it has a General section opened by default.
3. Scroll down and note the sections to control nullability and implicit imports, as shown in Figure 2.3:

Figure 2.3: Controlling project settings in the Visual Studio 2022 user interface

4. Close the project properties.

Verbs are methods

In English, verbs are doing or action words, like “run” and “jump.” In C#, doing or action words are called methods. There are hundreds of thousands of methods available to C#. In English, verbs change how they are written based on when in time the action happens. For example, Amir was jumping in the past, Beth jumps in the present, they jumped in the past, and Charlie will jump in the future.

In C#, methods such as WriteLine change how they are called or executed based on the specifics of the action. This is called overloading, which we’ll cover in more detail in Chapter 5, Building Your Own Types with Object-Oriented Programming. But for now, consider the following example:

// Outputs the current line terminator string.
// By default, this is a carriage-return and line feed.
Console.WriteLine();
// Outputs the greeting and the current line terminator string.
Console.WriteLine("Hello Ahmed");
// Outputs a formatted number and date and the current line terminator string.
Console.WriteLine("Temperature on {0:D} is {1}°C.", DateTime.Today, 23.4);

A different analogy is that some words are spelled the same but have different meanings depending on the context.

Nouns are types, variables, fields, and properties

In English, nouns are names that refer to things. For example, Fido is the name of a dog. The word “dog” tells us the type of thing that Fido is, and so to order Fido to fetch a ball, we would use his name.

In C#, their equivalents are types, variables, fields, and properties. For example:

• Animal and Car are types; they are nouns for categorizing things.
• Head and Engine might be fields or properties; they are nouns that belong to Animal and Car.
• Fido and Bob are variables; they are nouns for referring to a specific object.

There are tens of thousands of types available to C#, though have you noticed how I didn’t say, “There are tens of thousands of types in C#?” The difference is subtle but important. The language of C# only has a few keywords for types, such as string and int, and strictly speaking, C# doesn’t define any types. Keywords such as string that look like types are aliases, which represent types provided by the platform on which C# runs.

It’s important to know that C# cannot exist alone; after all, it’s a language that runs on variants of .NET. In theory, someone could write a compiler for C# that uses a different platform, with different underlying types. In practice, the platform for C# is .NET, which provides tens of thousands of types to C#, including System.Int32, which is the C# keyword alias int maps to, as well as many more complex types, such as System.Xml.Linq.XDocument.

It’s worth taking note that the term type is often confused with class. Have you ever played the parlor game Twenty Questions, also known as Animal, Vegetable, or Mineral? In the game, everything can be categorized as an animal, vegetable, or mineral. In C#, every type can be categorized as a class, struct, enum, interface, or delegate. You will learn what these mean in Chapter 6, Implementing Interfaces and Inheriting Classes. As examples, the C# keyword string is a class, but int is a struct. So, it is best to use the term type to refer to both.

Revealing the extent of the C# vocabulary

We know that there are more than 100 keywords in C#, but how many types are there? Let’s write some code to find out how many types (and their methods) are available to C# in our simple console app.

Don’t worry about exactly how this code works for now, but know that it uses a technique called reflection:

1. Delete all the existing statements in Program.cs.
2. We’ll start by importing the System.Reflection namespace at the top of the Program.cs file, as shown in the following code:

   using System.Reflection;
   

   Good Practice: We could use the implicit imports and global using features to import this namespace for all .cs files in this project, but since there is only one file, it is better to import the namespace in the one file in which it is needed.

3. Write statements to get the compiled console app and loop through all of the types that it has access to, outputting the names and number of methods each has, as shown in the following code:

   Assembly? myApp = Assembly.GetEntryAssembly();
   if (myApp == null) return; // quit the app
   // loop through the assemblies that my app references
   foreach (AssemblyName name in myApp.GetReferencedAssemblies())
   {
     // load the assembly so we can read its details
     Assembly a = Assembly.Load(name);
     // declare a variable to count the number of methods
     int methodCount = 0;
     // loop through all the types in the assembly
     foreach (TypeInfo t in a.DefinedTypes)
     {
       // add up the counts of methods
       methodCount += t.GetMethods().Count();
     }
     // output the count of types and their methods
     Console.WriteLine(
       "{0:N0} types with {1:N0} methods in {2} assembly.",
       arg0: a.DefinedTypes.Count(),
       arg1: methodCount, 
       arg2: name.Name);
   }
   

   N0 is uppercase N followed by the digit zero. It is not uppercase N followed by uppercase O. It means “format a number (N) with zero (0) decimal places.”

4. Run the code. You will see the actual number of types and methods that are available to you in the simplest application when running on your OS. The number of types and methods displayed will be different depending on the operating system that you are using, as shown in the following outputs:

   // Output on Windows
   0 types with 0 methods in System.Runtime assembly.
   44 types with 645 methods in System.Console assembly.
   106 types with 1,126 methods in System.Linq assembly.
   

   // Output on macOS
   0 types with 0 methods in System.Runtime assembly.
   57 types with 701 methods in System.Console assembly.
   103 types with 1,094 methods in System.Linq assembly.
   

   Why does the System.Runtime assembly contain zero types? This assembly is special because it contains only type-forwarders rather than actual types. A type-forwarder represents a type that has been implemented outside of .NET or for some other advanced reason.

5. Add statements to the top of the file (after importing the namespace) to declare some variables, as shown in the following code:

   using System.Reflection;
   // declare some unused variables using types
   // in additional assemblies
   System.Data.DataSet ds;
   HttpClient client;
   

   By declaring variables that use types in other assemblies, those assemblies are loaded with our application, which allows our code to see all the types and methods in them. The compiler will warn you that you have unused variables, but that won’t stop your code from running.

6. Run the console app again and view the results, which should look like the following outputs:

   // Output on Windows
   0 types with 0 methods in System.Runtime assembly.
   383 types with 6,854 methods in System.Data.Common assembly.
   456 types with 4,590 methods in System.Net.Http assembly.
   44 types with 645 methods in System.Console assembly.
   106 types with 1,126 methods in System.Linq assembly.
   

   // Output on macOS
   0 types with 0 methods in System.Runtime assembly.
   376 types with 6,763 methods in System.Data.Common assembly.
   522 types with 5,141 methods in System.Net.Http assembly.
   57 types with 701 methods in System.Console assembly.
   103 types with 1,094 methods in System.Linq assembly.
   

Now, you have a better sense of why learning C# is a challenge – because there are so many types and methods to learn. Methods are only one category of a member that a type can have, and you and other programmers are constantly defining new types and members!