My First Raspberry Pi Game – Part 02 – Saying hello

Parts: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12.

Writing your first ever computer program on the Raspberry Pi. See Part 1 for how to get and set up the Pi.

Today we will find out how to write a computer program, and how to run it.

We’re going to write one of the simplest programs you can write – we’re going to get the computer to say hello to us.

First, we need a text editor to write down our program. Click the weird aeroplane-y thing in the bottom left – that brings up the menu (like the Start button on Windows), then choose Accessories, then Leafpad. Leafpad is the text editor we will be using.

Leafpad will start, and show you an empty page. This is where we will write our program.

Type in exactly this:

print "Hello, world!"

and then click the File menu at the top of the Leafpad window and choose Save As. Click the word “pi” on the left and then click in the empty box next to the word Name, and type the name of our program, which is:

redgreen.py

“redgreen” is the name and the “.py” means this is a program written in the language Python. We’ll be finding out more about Python as we go on.

Click the Save button.

Our program is finished! Now we need to run it.

Click the aeroplane-y thing again, then Accessories, then LXTerminal. A terminal is a program you use to run other programs.

When LXTerminal has started, your cursor will appear next to a $ sign. This means it is ready for you to tell it what to do.

Type exactly this:

python redgreen.py

What this means is run the program called “python”, and pass the name of our program (redgreen.py) to it. This is how you run Python programs.

Now press the RETURN key.

If all goes well, our program will talk back to us, and say what we told it to say:

Hello, world!

Let’s look again at our program.

It’s just one “statement”, a print statement. A statement is something to do.

We pass one “argument” to print, “Hello, world!”. An argument is some information you give to a statement.

“print” doesn’t mean print to the printer, but write to the screen. So our program did exactly what we told it to do – it wrote our message to the screen.

Next time, we’ll map out the whole of our real program – a simple game.

Update: congratulations to sparkboy123 on getting this working!

My First Raspberry Pi Game – Part 01 – Before we start

Parts: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12.

In this series I intend to guide you through writing your first ever computer program.

We will write our own game on the Raspberry Pi, which is a cheap-as-chips computer designed for learning about computers.

Get a Raspberry Pi

To follow along, here’s what you will need:

  • A Raspberry Pi (about £25) – I got it from RS
  • An SD card (about £10) – be careful – not all of them work. I use: Kingston Technology 16GB
  • If your TV supports it, an HDMI cable (about £1) – I got: HDMI to HDMI Connector. If your TV doesn’t support HDMI, get a composite cable, but it won’t look as good or work as well.
  • A power supply (about £4) e.g. a smartphone charger (micro USB, at least 5V, 1A) – I got Micro USB Mains Charger but my existing HTC Wildfire S charger worked too.
  • USB keyboard and mouse (about £7) – I had them lying around, but a quick search suggests this one might be ok: CiT USB Keyboard and Mouse.

(Total cost, very approximately: £47)

Install “Raspian”

To use the Pi you will need to install some software onto your SD card.

To do this you will need a PC or laptop. If you don’t have one, or you’d prefer not to download and install software to an SD card, check out The Pi Hut. They sell SD cards that already have Raspian installed on them.

Raspian is the name of the software we will use to start up and run our Raspberry Pi. You need to download it and install it onto your SD card before you can put the SD card into the Pi and turn it on. To do this, you’ll need a way of writing to the SD card. Lots of laptops (and some desktops) have built-in SD card readers, or you can get a USB reader (I got this one: SD Card Reader USB 2.0).

To install Raspian “wheezy” (wheezy is the name of the latest version) go to the Raspberry Pi download page at www.raspberrypi.org/downloads and click the link in the Raspian “wheezy” section next to the words “Direct download”. Follow the instructions on how to install Raspian to your SD card here: elinux.org/RPi_Easy_SD_Card_Setup.

(There are also some helpful instructions here: reviews.cnet.co.uk/desktops/how-to-get-started-with-the-raspberry-pi-50009845/.)

Start the Pi

Once you’ve got an SD card with Raspian on it, insert it into your Pi (the SD card slot is underneath, which surprised me a bit). Plug the Pi into your TV by connecting the HDMI cable to it and plugging the other end into the TV’s HDMI port. Plug your keyboard and mouse into the 2 USB slots.

Take a deep breath, and plug the power supply into the micro-USB port.

If all goes well, some lights will appear on the Pi, you will be able to switch your TV to HDMI mode and your screen will show some writing and possibly pictures of raspberries. Wait for it all to settle down, and (hopefully) eventually you’ll see the setup screen.

First time setup

The first time your Pi boots it will ask you to do some setup. Read the raspi-config menu items and see whether there’s anything you want to change. You might want to change your keyboard and language settings, but I didn’t need to change anything at all. I just pressed TAB and then right-arrow to move onto the word Finish, then pressed RETURN.

There’s more information about how to set everything up at elinux.org/RPi_raspi-config, and there’s a nice detailed video here: First boot and Raspi-config.

Wait a bit more, and eventually you should see a huge raspberry, with a mouse cursor and desktop. If so, you’re ready for the next part!

Update: a real person really following this series!:

Tail Call Optimisation in C++ – lightning talk video

You can watch the Tail Call Optimisation in C++ lightning talk video, which I gave at the ACCU 2012 conference in April.

You can also read the (clearer and more correct) writeup I did later: Tail Call Optimisation in C++ or the subsequent article published in Overload 109.

Scheme 7: Macros video

Series: Feel the cool, Basics, Closures, Recursion, Quotation, Lambda, Macros.

Continuing the series on Scheme, this video explains the ultimate alternative – when nothing else is flexible enough, we can create our own bits of lanugage using macros.

Slides for Scheme 7: Macros

Scheme 6: Lambda video

Series: Feel the cool, Basics, Closures, Recursion, Quotation, Lambda, Macros.

Continuing the series on Scheme, this video explains the lambda function, which allows you to define anonymous functions. It goes on to bend your mind with 2 examples of the enormous power of functions and closures in Scheme.

Slides for Scheme 6: Lambda