# Lesson 1: Hello, World!

{% hint style="warning" %}
At the end of this lesson, you should be able to answer the following:

* What is a statement?
* How do I display a message on the screen using C#?
  {% endhint %}

Let's make our program print a message. We're going to print out "Hello, World!" to the console. 

A console (also known as terminal) is a text-only display or environment that enables us to interact with the computer.

{% hint style="info" %}
**Did you know?**

The ["Hello, World!" program](https://en.wikipedia.org/wiki/%22Hello,_World!%22_program) is traditionally the first program written by people who are learning to code.
{% endhint %}

To make our C# program print a message, we'll use a command called `Console.WriteLine()`.

The message you want to display goes inside the round brackets `()`. We also need to put the message inside double quotes, like this:

**`"Hello, World!"`**

In the code box on your notebook, type the following:

```csharp
Console.WriteLine("Hello, World!");
```

This line of instruction is called a *statement*. C# programs are made up of statements. 

Statements end with a semicolon (`;`). Think of a statement like a sentence: the semicolon is equivalent to the full stop or period. 

If there were no full stops, the reader (in our case, the C# compiler) will have trouble understanding us, since it doesn't know where our sentences begin and end.

Next, run the program by clicking on the Execute button on the code box.

![The location of the Execute button](https://3447149067-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-MdynmZrfNEt1WSSrlHq%2F-MdzSyBCvYBuu4tEQ6EI%2F-MdzgEelJfEJ4VHO19O8%2F2021-07-07_16-37-12.png?alt=media\&token=c77e16a9-e4cb-4261-95d2-819f2d1a81fb)

The output of the program will be shown at the bottom of the code box.

![](https://3447149067-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-MdynmZrfNEt1WSSrlHq%2F-Me-KqqBb-FL1kzNa3Ry%2F-Me-LyaLW-EUoLWExOL6%2F2021-07-07_19-44-37.png?alt=media\&token=ae51ba10-dea5-4662-8921-d7c7c9ecc08e)

**Congratulations**! You have written and run your first C# program.

Let's display another message. Write `I'm learning C#`! to the console.

After the first `Console.WriteLine()`, press Enter to go to a new line and type the next statement.

```csharp
Console.WriteLine("I'm learning C#!");
```

The full program should look like this:

```csharp
Console.WriteLine("Hello, World!");
Console.WriteLine("I'm learning C#!");
```

Run the program again by clicking the Execute button.

Your output should look like this:

![](https://3447149067-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-MdynmZrfNEt1WSSrlHq%2F-Me-KqqBb-FL1kzNa3Ry%2F-Me-Rr8OTr32vLt4bWbS%2F2021-07-07_20-09-53.png?alt=media\&token=d6daaa4a-5367-4f3e-8750-f6bd668ea5ce)

As you may have noticed, statements run **in sequence**. If you placed `I'm learning C#!` before the `Hello, World!` statement, the output would be different.

{% hint style="success" %}
**Tip**

You may have noticed a box popping up while typing. This feature is part of [**IntelliSense**](https://code.visualstudio.com/docs/editor/intellisense), a helpful tool for writing code. It provides hints, suggestions, and documentation for your code.
{% endhint %}

![IntelliSense at work](https://3447149067-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-MdynmZrfNEt1WSSrlHq%2F-Me-KqqBb-FL1kzNa3Ry%2F-Me-SqvABvLARJR-lpxj%2F2021-07-07_20-08-35.png?alt=media\&token=18acbbd6-74e5-4196-83a7-ee884b41bd2a)

{% hint style="info" %}
**Question**

What happens when you remove the semicolon from the end of the statements? Will the program run?

```csharp
Console.WriteLine("Hello World")
Console.WriteLine("I'm learning C#!")
```

{% endhint %}

{% hint style="info" %}
**Question**

Can you spot the error in this program? (If you're stuck, copy and paste this to the code box. The squiggly red lines will show you where the error is!)

```csharp
Console.WriteLine(Hello World!);
```

{% endhint %}

{% hint style="info" %}
**Challenges**

1. Introduce yourself to the computer! Display the message **`Hi! My name is <NAME>`**. Replace **`<NAME>`** with your name, of course.
2. Print out your favourite haiku (Japanese poem) on the console. If you don't have one, use one of the examples [here](https://examples.yourdictionary.com/examples-of-haiku-poems.html). Each line of the haiku should be printed on its own line.
   {% endhint %}


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