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Learn about the C# programming language: what is it, how it's used, and why you should learn it.

Hello World

Congrats! You finished your first lesson in C#. In this lesson you learned:
* C# is used to make interactive websites, mobile apps, video games, augmented and virtual reality (AR and VR), back-end services, and desktop applications
* .NET generally refers to the family of programs and commands that let you make applications with C#
* C# and .NET jobs are out there! Build video games with [Unity](https://unity.com/), build websites with [ASP.NET](https://dotnet.microsoft.com/apps/aspnet)...The skills you learn on Codecademy can open new doors
* The command `Console.WriteLine()` prints text to the console
* The command `Console.ReadLine()` captures user input in the console
* _Comments_ are lines of code that are ignored by your computer; they're intended to be read by developers instead. Make them with `//` or `/*` and `*/`


Review

We can also read input from a user. The command `Console.ReadLine()` captures text that a user types into the console.  

<img src="https://content.codecademy.com/courses/learn-c-sharp/hello-world/dotnet-run-ex.gif" title="Getting input with C#" alt="Program: How old are you? User: 16 Program: You are 16 years old!">
<br>

In this example, the program writes a question to the console and waits for user input. Once the user types something and presses <kbd>Enter</kbd> (or <kbd>Return</kbd>), the input is printed back out to the user. 
```cs
Console.WriteLine("How old are you?");
string input = Console.ReadLine();
Console.WriteLine($"You are {input} years old!");
```


The word `input` represents a variable (variables are explored more in other lessons). For now, know that the word `input` represents the text the user typed in the console. It's labeled `string` because, in C#, a piece of text is called a `string`. 

`input` is used in the following line so that the printed message will change based on what the user types. For example, if you ran the program and responded to the question with `101`, then the value of `input` would be `"101"` and `You are 101 years old!` would be printed to the console.

 Getting Input

What would you like to build? If you can name it, you can probably build it with C#.

This programming language can be used to make interactive websites, mobile apps, video games, augmented reality (AR), virtual reality (VR), desktop applications, and back-end services – just to name a few. For example, the mobile game [Pokemon Go](https://en.wikipedia.org/wiki/Pok%C3%A9mon_Go) and the [Stack Overflow website](https://stackoverflow.blog/2008/09/21/what-was-stack-overflow-built-with/) were built with frameworks that can be run with C# (Unity and ASP.NET, respectively).

Even if you already know a programming language, learning C# (pronounced “cee sharp”)  can make you a better programmer: 
* Unlike languages like Ruby and JavaScript, C# has you define the _type_ of each data in a program. Assigning a type essentially tells a computer what operations can and cannot be performed on a piece of data. This style of coding helps programmers avoid a large class of errors that are common to Ruby and JavaScript .

* If you're familiar with Java, you'll recognize how C# programs are built&mdash;by defining objects that interact with each other, which makes code reusable and easy to manage. 

C# can be used to make interactive websites, mobile apps, video games, augmented reality (AR), virtual reality (VR), desktop applications, and back-end services

What is C#?

Time to run some C# yourself! 

There are two panels here: a text editor containing some C# code and a console, or terminal, that shows output. When you run the code, you'll see some text printed to the console. 

The code is contained in a file called **Program.cs**. For now, just focus on the line: 

```cs
Console.WriteLine("Hello World!");
```

`Console.WriteLine()` is a command that prints text to a console. Whatever is in between the parentheses will be printed to the console!  In this case it's `Hello World!`.

Run Some C#

Ironically, an essential tool in programming is the ability to tell a computer to <u>ignore</u> a part of a program. Text written in a program but not run by the computer is called a _comment_. In C#, anything after a `//` or between `/*` and `*/` is a comment. In spoken word we call these symbols "forward slashes" and "asterisks".

Comments can: 

 * Provide context for why something is written the way it is:
```cs
/* This variable will be used to count the number of times anyone tweets the word persnickety */
int persnicketyCount = 0;
```

 * Help other people reading the code understand it faster: 
```cs
/* Calculates tomorrow's rain likelihood as a number between 0 and 100 */
ComplicatedRainCalculationForTomorrow();
```

 * Ignore a line of code and see how a program will run without it:
```cs
// string usefulValue = OldSloppyCode();
string usefulValue = NewCleanCode();
```

Developers tend to use `//` for short, one-line comments and `/* */` for anything longer, but the choice is up to you!

Comments

You've seen some examples of C# code in action, but learning a programming language is more than just memorizing commands: it's understanding how it differs from other technologies, joining its community, and applying it to real-life problems. Here's what you need to know:

1. C# technologies are fast: A software company called [Raygun](https://raygun.com/blog/dotnet-vs-nodejs/) built their application using Node.js, a framework for JavaScript. When their app started to slow down, they switched to  .NET, a framework for C#. Their performance skyrocketed. As CEO John Daniel puts it, "using the same size server, we were able to go from 1,000 requests per second...with Node.js, to 20,000 requests per second with .NET Core." In other words, they increased throughput by 2,000%.

2. The C# community is big: In 2019, [Github ranked C# as the fifth most popular programming language](https://octoverse.github.com/#top-languages) and [StackOverflow ranked it seventh](https://insights.stackoverflow.com/survey/2019#most-popular-technologies).

3. C# is employable: Thanks to good design and the popularity of frameworks supporting the language, C# can get you access to a lot of great jobs. Search on any job site and you'll find companies looking for C# and .NET developers to build chat applications, financial trading programs, medical record systems, and beyond. In the 2019 HackerRank Developer Skills Report, expertise in [two C#-compatible frameworks, ASP.NET and .NET Core, were among the top ten most sought-after by managers](https://research.hackerrank.com/developer-skills/2019#skills).



