intro-to-dotnet-web-dev/2-csharp/README.md

# 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!