# C# Crash Course 🚀 In this C# Crash Course, we'll go over the basics of C# so that you'll be ready to build out exciting web apps! We'll start by going through the key attributes of C#, syntax basics, and introduce you to OOP. In each section, we'll link you to some quick in-browser C# challenges so you can apply these concepts. ## Topics you'll learn * Language attributes * Syntax basics * Object Oriented Programming --- # Language attributes C# is a strongly typed, compiled, object oriented language. Let's break this down. ## Strongly typed In a **strongly typed** language, every variable has a defined type. Some of these types include: * String, "Hello world!" * Char, 'a' * int, 3 * decimal, 1.5 * bool, True ## Compiler A **compiler** converts the code you write into a format that your computer can understand. After you write C# and build it, the C# compiler (called Roslyn) will analyze your code to check for any errors. --- # The basics ## 🌍 Hello World Here's a piece of code that will print "Hello world!" to the console. ```csharp using System; Console.WriteLine("Hello world!"); ``` ## Keywords With C#, you use keywords like `using` and `Console`. **Keywords** are predefined, reserved identifiers that have special meanings to the compiler. ## Accessing methods The `. (DOT)` in `Console.WriteLine` allows us to access methods and properties. In this example, `Console` is a type that represents the console window. `WriteLine` is a method of the Console type that prints a line of text to that text console. ## Parameters In this example, we use parentheses pass a string as a parameter to `Console.WriteLine`. ## 🚨 Challenge 1 Time for your first challenge! | # | Challenge | Solution | Duration | What you will learn | More information | |-| ------------------------------- | ------------------------------- | ----------- | -------------------------------------- | - | 1 | [Hello World Challenge](https://docs.microsoft.com/learn/modules/csharp-write-first/2-exercise-hello-world/?ns-enrollment-type=learningpath&ns-enrollment-id=learn.languages.csharp-first-steps)| N/A | 3 min | case sensitive, strings, comments | [Intro to C# Tutorial](https://docs.microsoft.com/dotnet/csharp/tour-of-csharp/tutorials/hello-world?WT.mc_id=csharpnotebook-35129-website), [C# documentation](https://docs.microsoft.com/dotnet/csharp/) | ## Variables In C#, **variables** allow you to temporarily store a value in memory. In C#, you must declare a variable before using it. ```csharp var cSharp = "really cool"; ``` In this example, we created a string called `cSharp`. You can use the var keyword to declare local variables without explicitly giving them a type. Variable names can contain alphanumeric characters and underscores, but no special characters. They also cannot be keywords. ## 🚨 Challenge 2 | # | Challenge | Solution | Duration | What you will learn | More information | |-| ------------------------------- | ------------------------------- | ----------- | -------------------------------------- | - | 2 | [Variables Challenge](https://docs.microsoft.com/learn/modules/csharp-literals-variables/6-challenge )|[Solution](https://docs.microsoft.com/learn/modules/csharp-literals-variables/7-solution)| 5 min | variables, data types, strings, ints, decimals | [String formatting tutorial](https://docs.microsoft.com/learn/modules/csharp-basic-formatting/), [C# documentation](https://docs.microsoft.com/dotnet/csharp/) | # Syntax cheat sheet ## Semicolons Every statement is ended by a semicolon ```csharp Console.WriteLine("there is a ';' at the end of this statement"); ``` ## Comments You can make comments by using 2 slashes ```csharp // this is a comment is C# ``` ## Case sensitive C# is case sensitive! For example, a variable "cat" is completely different from a variable "CAT". ```csharp var cat = "meow"; ``` ```csharp var CAT = "rawr"; ``` ## Arithmetic Operators These are probably familiar to you! | symbol | what it does | | --- | ------ | | + | addition | | - | subtraction | | * | multiplication | | / | division | | % | remainder | | ++ | increment | | -- | decrement | ## 🚨 Challenge 3 | # | Challenge | Solution | Duration | What you will learn | More information | |-| ------------------------------- | ------------------------------- | ----------- | -------------------------------------- | - | 3 | [Operating on numbers challenge](https://docs.microsoft.com/learn/modules/csharp-basic-operations/5-challenge)|[Solution](https://docs.microsoft.com/learn/modules/csharp-basic-operations/6-solution)| 2 min | ints, decimals | [Number operations tutorial](https://docs.microsoft.com/learn/modules/csharp-basic-operations/), [C# documentation](https://docs.microsoft.com/dotnet/csharp/) | ## Decision logic In C#, you can build applications that employ decision-making logic so that your application performs different instructions based on a set of conditions. One way we do this is with an `if` statement. `if` statements are made up of three parts: * The if keyword * A Boolean expression between parenthesis () * A code block defined by curly braces { } If there are multiple condition, you can utilize the `else if` and `else` statements. Basically, if the `if` statement fails, these other statements allow you to test against other conditions. You can imagine this in the context of a rock⛰️-paper📃-scissors✂️ game. Imagine you chose rock⛰️. * `if` your opponent chooses scissors✂️, then you will win * `else if` your opponent also chooses rock⛰️, then you will tie * `else` your opponent chooses paper📃, then you will lose Each possible decision your opponent could make leads to a different outcome. ## Boolean expressions Booleans are expressions that return either `true` or `false`. They are often used to compare two or more things. | symbol | what it does | | --- | ---------- | | < | less than | | > | greater than | | <= | less than or equal | | >= | greater than or equal | | == | equal | | != | not equal | ## 🚨 Challenge 4 | # | Challenge | Solution | Duration | What you will learn | More information | |-| ------------------------------- | ------------------------------- | ----------- | -------------------------------------- | - | 4 | [Decision logic challenge](https://docs.microsoft.com/learn/modules/csharp-if-elseif-else/4-challenge)|[Solution](https://docs.microsoft.com/learn/modules/csharp-if-elseif-else/5-solution)| 2 min | if, else if, else, booleans | [Boolean expressions tutorial](https://docs.microsoft.com/learn/modules/csharp-evaluate-boolean-expressions/1-introduction), [C# documentation](https://docs.microsoft.com/dotnet/csharp/) | --- # Object Oriented Programming C# is an object-oriented language. Objects are defined by **Classes**. In other words, an **Object** is an instance of a class. One way to think about this is that a class is like the blue prints for a house. The actual house that is built is an objects because it is an instance of this blue print. ## Properties and methods Objects inherently have attributes. In C# we call these **properties**. The attributes of a house may be the number of doors, what color the house is painted, etc. We can also define **methods** which describe what an object can do. For example, you can sell your house. To summarize these concepts using our house example, A Class is like a blueprint 📜 An Object is an instance of this blueprint, or a house 🏠 The Properties of a house could be the number of doors it has or the color it's painted 🚪 🎨 A Method of our class is that we can sell our house 💸 Let's look at an example House class: ```csharp // The namespace declaration provides a way to logically organize your classes namespace Classes; public class House { // House properties public string Address { get; } public int Size { get;} // House methods public void SellHouse(decimal amount, DateTime date) { } } ``` ## Constructor We can define a **constructor** to allow us to create new House objects. ```csharp public House(string address, int squareFeet) { this.Address = address; this.Size = squareFeet; } ``` When we create an object with `new` this constructor will be called. ```csharp using Classes; // Let's create a 1500 square foot house on Candy Cane Lane var house = new House("123 Candy Cane Lane", 1500); ``` ## The .NET Class Library C# also has built in classes and functionality within the .NET Class Library. The .NET Class Library is a collection of thousands of classes containing tens of thousands of methods. These methods are created by Microsoft and are available for use in your applications. For example, when we called `Console.WriteLine` earlier, we were calling a method from the `System.Console` class. For a more in-depth overview, you can read up on the .NET Class Library in the [.NET documentation](https://docs.microsoft.com/dotnet/standard/class-library-overview). ## 🚨 Challenge 5 | # | Challenge | Solution | Duration | What you will learn | More information | |-| ------------------------------- | ------------------------------- | ----------- | -------------------------------------- | - | 5 | [.NET Class Library challenge](https://docs.microsoft.com/learn/modules/csharp-call-methods/5-challenge)|[Solution](https://docs.microsoft.com/learn/modules/csharp-call-methods/6-solution)| 2 min | ints, decimals | [.NET documentation](https://docs.microsoft.com/dotnet/standard/class-library-overview), [C# documentation](https://docs.microsoft.com/dotnet/csharp/) | # Bonus and more ways to connect Want more practice with C#? The .NET team has you covered. Here's a few learning resources: * C# Video Series on [Microsoft Docs](https://docs.microsoft.com/shows/CSharp-101/?WT.mc_id=dotnet-35129-website) or [YouTube](https://www.youtube.com/watch?v=Z5JS36NlJiU) * Self Guided Tutorials on [Microsoft Learn](https://docs.microsoft.com/users/dotnet/collections/yz26f8y64n7k07) * [Learn to Code Page](https://dotnet.microsoft.com/learntocode) Connect with us! Check out the [.NET Community Page](https://dotnet.microsoft.com/platform/community) to find links to our blogs, YouTube, Twitter, and more. # How'd it go? Please take this quick, [10 question survey](https://aka.ms/WebLearningSeries-git-survey) to give us your thoughts on this lesson & challenge!