C# Crash Course

When I want to learn a new language, there's usually a series of steps I'll take before I can be productive. I'm writing this article based on what I'd find useful if I wanted to learn C# from scratch.

I'll be focusing on .NET Core in this post. It's cross-platform and open source.

Index

Things to download

Once the above have been installed, your computer is ready for C# development. To verify, open your terminal and run:

dotnet --version

At the time that I'm writing this, my version is 3.1.403.

Your first project

Now that we have that out of the way, let's get a new project started:

  1. Create a folder somewhere, call it HelloWorld.
  2. Open that folder in vscode. (You can start vscode and drag the folder on top of it.)
  3. Toggle the integrated terminal using the Ctrl + ` (Backtick).
  4. Enter the following command:
dotnet new console
  1. At this point you will have your initial Hello World program. You can run it using:
dotnet run

You should see Hello World! printed in the terminal.

  1. Open the Explorer using Ctrl + Shift + E
  2. Open Program.cs to see the source code. You should see:
using System;

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

The first line imports the System library. That gives you access to Console later.

After that a namespace is started. It's a good practice to keep all your code in namespaces. The namespace here is HelloWorld. You can name it anything you want.

Inside the namespace, a class is defined called Program. You can name your classes anything you want.

Inside the Program class there's a static function called Main. Main is your program entry point. When you called dotnet run earlier, it specifically looked for it.

Lastly, there's the WriteLine function call on the Console class. Console is a static class which means you don't need an instance of it.

To run your program through the vscode debugger, press F5 and select .NET Core if prompted. That will generate a .vscode folder that contains the launch configuration. To check that the debugger works, you can add a breakpoint. Put your cursor on the Console.WriteLine("Hello World!"); line and press F9. Now press F5 and the program will pause on that line. You can press F5 to resume the execution.

Types

C# is a typed language. Here are some of the built-in types:

bool isHappy = true;
int num = 10;
float ratio = 3.4f;
double humanCount = 2.5d;
char c = 'c';
string whatName = "What is your name?";

You can declare your variables directly in your class' scope or functions:

namespace HelloWorld
{
    class Program
    {
        static void Main(string[] args)
        {
            int num = 10;

            int result = num * 2;
        }

        string whatName = "What is your name?";
    }
}

Note that you first declare the type, then the variable name before assigning a value.

Methods

You can declare methods in your class:

using System;

namespace HelloWorld
{
    class Program
    {
        static void Main(string[] args)
        {
            Program p = new Program();
            int num = p.AddFive(10);

            Console.WriteLine(num);
        }

        public int AddFive(int a)
        {
            return a + 5;
        }

        string whatName = "What is your name?";
    }
}

Since the AddFive function is not static, I created an object instance of the Program class so that I could access it. I called the instance p. I stored the result in the num variable and printed that out.

Notice the public keyword. When public isn't there, the default is private. For example whatName is currently private. That means you can't do p.whatName to access it.

If

To make everything more interesting, you can use an if statement.

using System;

namespace HelloWorld
{
    class Program
    {
        static void Main(string[] args)
        {
            int num = 5;

            if (num > 10)
            {
                Console.WriteLine("Num is bigger than 10!");
            }
            else if (num < 5)
            {
                Console.WriteLine("Num is smaller than 5.");
            }
            else
            {
                Console.WriteLine("Num is 5!!!");
            }
        }
    }
}

Here is a list of comparison operators: ==, <=, <, >=, >, !=

Loops

Here are a few loops:

// for loop
for (int i = 0; i < 5; i++)
{
    Console.WriteLine("Count: " + i);

    // You can also use an interpolated string:
    Console.WriteLine(
quot;Count:
{i}"
); } // while loop int i = 0; while (i < 5) { Console.WriteLine(
quot;Count:
{i}"
); i += 1; } // foreach loop int[] nums = {0, 1, 2, 3, 4}; foreach (int n in nums) { Console.WriteLine(
quot;Count:
{n}"
); }

Classes

You can separate your code into many classes. You can have multiple classes in one file, or you can split them into many files.

using System;

namespace HelloWorld
{
    class Program
    {
        static void Main(string[] args)
        {
            Welcome w = new Welcome("Hello my good friend");

            w.GreetName("Jean-David");
        }
    }

    class Welcome
    {
        public Welcome(string message)
        {
            _message = message;
        }

        public void GreetName(string name)
        {
            Console.WriteLine(
quot;
{_message} {name}"
); } // It's a good practice to prefix private fields with an underscore. private string _message; } }

Some notes on the C# Coding Standards and Naming Conventions. I personally don't follow it 100%, but it's a good starting point.

NuGet

When working with C#, you'll often want to integrate various libraries in your projects. Let's refactor the previous example to accept a name from the launch arguments. That will allow you to start the application with HelloWorld -n Jean-David.

There's a good library that makes this task be pretty trivial called CommandLineParser. If you look on that page, there's a tab for .NET CLI. It will give you the command that will install the CommandLineParser package:

dotnet add package CommandLineParser --version 2.8.0

After running that command, if you open the HelloWorld.csproj file, you will see:

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>netcoreapp3.1</TargetFramework>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="CommandLineParser" Version="2.8.0" />
  </ItemGroup>

</Project>

Now look back in the CommandLineParser NuGet page and you'll see there's a PackageReference tab. That tab shows what to add to the .csproj file if you wanted to install a package manually without the CLI.

If you edit the packages in a .csproj, you then have to run a restore:

dotnet restore

Let's change the previous example to:

using System;
using CommandLine;

namespace HelloWorld
{
    class Program
    {
        public class Options
        {
            [Option('n', "name", Required = true, HelpText = "Set the name to welcome.")]
            public string Name { get; set; }
        }

        static void Main(string[] args)
        {
            Parser.Default.ParseArguments<Options>(args)
                .WithParsed<Options>(o =>
                {
                    Welcome w = new Welcome("Hello my good friend");
                    w.GreetName(o.Name);
                });
        }
    }

    class Welcome
    {
        public Welcome(string message)
        {
            _message = message;
        }

        public void GreetName(string name)
        {
            Console.WriteLine(
quot;
{_message} {name}"
); } private string _message; } }

You can run the application with:

dotnet run -n Jean-David

If you want to be able to debug the application, you'll need to edit your vscode launch.json file. Open .vscode/launch.json. Edit the configuration to add the args in the array:

{
    "name": ".NET Core Launch (console)",
    "type": "coreclr",
    "request": "launch",
    "preLaunchTask": "build",
    "program": "${workspaceFolder}/bin/Debug/netcoreapp3.1/HelloWorld.dll",
    "args": ["-n", "Jean-David"],
    "cwd": "${workspaceFolder}",
    "console": "internalConsole",
    "stopAtEntry": false
},

Conclusion

If you liked this crash course or want to give me some feedback, feel free to drop by the Discord: https://discord.rashtal.com/.


TODO:

  • Where to find help.