An Introduction to Programming

• hackety
• beginner

Hello there!

Round One

So, you'd like to learn how to hack code with the best of 'em, eh? Well, you've come to the right place. This is the very first lesson I have to share with you. It all starts here.

I want to get you started off on the best possible foot with making programs, so we'll start off by talking a little bit about what programming is, and then we'll write some basic programs to draw fun things on the screen. Sound good? Off we go!

Let's talk about programming

It's all about instructions

When you get down to it, programming is all about algorithms. That's a big fancy word for 'a list of instructions.' Every program is simply a big to-do list of instructions for the computer to follow.

You can turn almost anything into a list of instructions if you really think about it. Most of the time, you've got so much practice at doing things that you don't even think about these individual steps. You just do them. It's very natural.

The computer is simple

Unfortunately, computers are actually quite simple. This may be contrary to everything you've ever heard, but it's the truth. Even though we compare computers to things like our brains, it's a really poor analogy. What computers are actually really good at is performing simple, boring things over and over again very accurately. They can't think for themselves!

This is why computers appear to be complex. They blindly follow whatever orders they're given, without any thought about how those instructions are good or bad. It's hard to think in such simple terms!

Explain yourself well

It's important to remember that you have to fully explain yourself to the computer when you're programming. It can't figure out what you're trying to say, so you have to say what you mean!

This takes some practice, so we're going to start off with some exercises in explaining ourselves in very basic terms. It's almost like trying to explain math to a young child: you have to go slowly, triple check your work, and have some patience when it just doesn't quite get it.

Lists of Instructions

A to-do list, not a shopping list

When I say that computers follow lists of instructions, I mean a to-do list, not a shopping list. What I'm trying to say is that these lists have an order to them that the computer follows. It does each step in turn as quickly as it possibly can.

A shopping list is a different kind of list entirely. You can go to whichever aisle you choose, and as long as you get everything before you leave, you're A-OK. This isn't what the computer does at all.

How would you tell a person to do it?

Let's try an example: if you had to tell someone in words how to draw a square on a piece of paper, how would you do it?

You're not allowed to say "like this" or "this way," that's cheating! You have to spell out every detail.

Once again: computers are simple

How'd you do? I can't see what you said, but here's an example of how simple computers are compared to people. Did you forget to mention how long each side of the square is? If you didn't good job!

Here's how I'd do it, by the way. This isn't the only right answer, it's just an example:

1. Put your pen down on the paper.
2. Draw right one inch.
3. Draw down one inch.
4. Draw left one inch.
5. Draw up one inch.
6. Take your pen off of the paper.
7. Finished!

Turtles, all the way down.

Drawing... with turtles?

Okay! Enough of these thinking experiments. Let's actually make something. I bet you've been wondering when that was going to start, right? It's really important to get the basics down first.

We're going to tell the computer how to draw shapes... with turtles. Yes, you heard me right. You're going to have to give these instructions to a turtle.

This particular turtle is carrying a pen. You have a piece of paper. The turtle will follow your every word. But the turtle is a bit slow, and needs careful instruction. Are you up to it?

The Turtle and its commands

We have to tell Hackety Hack that we want to tell the Turtle what to do. To do that, we have a Turtle command. We can tell the Turtle two things:

draw: the turtle will follow our instructions at lightning speed,

start: an interactive window will appear, which lets you see the turtle move at each step in the program. You can move at your own pace. This is useful if the turtle isn't doing what you expect!

Click on the editor tab to get started:

Type it in!

Cool. Now type this:

Turtle.draw

The period in between the Turtle and the draw connects them together. Programming languages have rules, just like English has rules! You can think of Turtle like a subject, and draw as a verb. Together, they make a sentence: hey turtle, draw me something!

Once you've typed that in, go ahead and click the 'Run' button. The turtle moves so quickly in draw mode that you won't even see him, but I assure you, he's there!

Do... what I tell you to

Awesome! We've got the turtle going, at least. Now we need to tell it what we want to draw!

Remember when we said that all programs are lists of instructions? In this case, our program only has one instruction: Turtle, draw something! But we need to be able to give the Turtle its own list of instructions.

To do this, we'll use two words: do and end. These two words together make up a sublist of things, just for the Turtle!

Changing the background

Let's try this: we can tell the Turtle that we want to use a different background color by using the background command. Check it out:

Turtle.draw do
  background maroon
end

Type this in and click 'Run'!

The Turtle gets its orders

Cool stuff! The background is now maroon. You can find a full list of colors that are supported on the Shoes website.

This is also how you make lists of instructions for the Turtle to follow. To make it a little easier to see, programmers will often put two spaces before sublists. Get in the habit now, you'll thank me later!

The pen

Now that we've got a snazzy background color, how do we draw some lines? Well, the first thing you need to know about is the pen. The Turtle carries a pen along, and drags it along the ground behind itself. You can change the color of line the pen draws with the pencolor command.

Drawing lines

Sally forth!

Okay, enough dilly-dallying. Let's tell the turtle to draw a line! Here's my line. Give this one a shot, then try your own colors and numbers!

Turtle.draw do
  background lightslategray
  pencolor honeydew
  forward 50
end

50 is the number of pixels to move foward, by the way.

You spin me right round, baby

Great! So you've got a line. But what if you don't want the Turtle to move forward? Well, you can tell it to turn by using a turnleft or turnright command, like this:

Turtle.draw do
  background lightslategray
  pencolor honeydew
  forward 50
  turnright 90
  forward 50
end

Give that a shot, then play with it a bit!

If you're wondering what 90 means, it's the number of degrees that it'll turn.

I like to move it, move it

Okay, now we're cooking! Let's break this down again:

Turtle.draw tells the Turtle we want it to draw some things. The period connects the two.

do ... end is a sublist of things. This is what we want the Turtle to be drawing. Not for the rest of our program.

pencolor sets the color of the pen the Turtle is dragging along behind him, and background sets the color of the background.

turnright (or its buddy turnleft) tells the Turtle to turn to the right or left.

forward (or its friend backward) tells the Turtle to move.

Let's try drawing that square

Go ahead. Give it a shot. Try to get the Turtle to draw a square.

I'll wait. :)

Here's my version

Here's how I did it:

Turtle.draw do
  background lightslategray
  pencolor honeydew
  forward 50
  turnright 90
  forward 50
  turnright 90
  forward 50
  turnright 90
  forward 50
end

Repeating ourselves

Pete and Repeat...

Man, that was a ton of reptition! My fingers almost fell off typing forward and turnright there!

I have good news, though: I mentioned something earlier about computers. It turns out that doing boring, repetitive things is something they're really good at! They'll do the same thing over and over again, forever even as long as you ask nicely.

Repeating repeating ourselves ourselves

Check it out: our Turtle actually knows numbers. For example:

Turtle.draw do
  background lightslategray
  pencolor honeydew
  4.times do
    forward 50
    turnright 90
  end
end

Try running this example. It also draws a square! Wow!

4.times

It's pretty easy: 4 can take instructions too, just like our Turtle. This command repeats a list of instructions that many times. Fun! Four times. And the do and end show which list of instructions go with the 4 rather than with the Turtle.

Try it out!

Have a blast: make some fun shapes of your own!

Summary

Congratulations!

Wow, you're awesome. Pat yourself on the back. High five someone. You've got these basics down!

Check out the Basic Ruby lesson to pick up some totally different and exciting things!