Intro to Arrays (Video Version)

This is an introduction to arrays and how to use them to store multiple numbers or strings. This also introduces how to get information about arrays, such as the length of the array.

You already learned about using variables
to store numbers or strings.

Now we're going to learn
about something called arrays,

which let us store multiple items
in just one variable.

As you'll see, arrays let us do
all kinds of useful things.

Okay, let's review variables. All right?

So we have, var myFriend = "Sophia".

So, a variable is just a way
of storing a value, like Sofia,

and giving it a label so our program
has an easy way to refer to it later.

We can think of it like a drawer,

with a myFriend label on the outside
and Sofia on the inside.

So whenever we look inside it,
we find Sofia.

Now, sometimes we want to hold
multiple values in a single variable

and we can't just do it like this
because we'll get a syntax error

and our program will freak out,
and all that stuff.

So we have a specific way
that we do that,

and that's using arrays.

So we could say, myFriends = ,

and then we have to do
a square bracket,

and then inside,
that's where we can put all the values.

So we say, Sofia,
and we have John, and we have Leif.

All right, so those are my three friends.

Maybe in order of how much I like them,
but don't tell them that.

Okay, so now our variable
holds three values, not just one.

And we can imagine
it's like a chest of drawers,

and we put this label, myFriends,
on the whole chest.

And we can just open the right drawer

to find the value
we're looking for, right?

And you imagine, with a chest of drawers,

if you want to know
what's inside the first drawer,

you would just open it up and look inside.

So how do we do that with our array?

Well, we can just type
the name of the array,

and then the brackets again--

ooh, I misspelled it--

and then the number
of whatever it is in the array, right?

So maybe it would be 1. Okay?

So, let's actually try this out

by using the text command
and showing Sofia on the canvas.

So we say, myFriends--
ooh, friend is a hard word to spell, huh?

So, myFriends[1],
and then we put it here.

Oh, and then let's put a little fill.

Oh, okay, so we see John.
Why do we see John?

We said 1 for the element index, right?

The 1 right here.

Well, that's because
arrays start at 0, not 1,

and it'll definitely seem weird at first,
but you'll get used to it.

So if we put 0,
then we see Sofia, all right?

And then, if we want to show
the next element,

then we use 1, all right?

So, and then if we want to do
the final element,

the third element, then we use 2.

So you just think to yourself:
"Okay, which one do I want to retrieve?"--

Oh, let's spread these out--

and where is it located,
and you just subtract one.

So the first one is 0,
the second one is 1,

the third one is 2, et cetera, et cetera.

What happens if I forgot,
and I try to access Leif this way?

Well then, we say myFriends[3],
and we'll just get nothing.

That's because there's nothing there, right?

When it says 3,
it looks for the fourth element,

and there's no fourth element,
so there's just nothing.

And that's something that can happen a lot
when you're using arrays,

so just look out for that.

And the same thing
if I tried to access a hundred

because I don't have a hundred friends,
I only have three,

so then we get nothing, all right?
So let's get rid of those.

Now, let's say we want to keep track
of how many friends we have

because I'm really proud,
and I have three friends,

and I want to let everybody know.

So I'm going to go
and declare this to the world.

So, "I have " + numFriends + " friends!!!".

Woo, all right.

Okay, so I have three friends. Yay!
Oh, that's not very many.

Okay, so maybe Winston feels bad for me
and says he'll be my friend,

and he says I can add him to the array.

And I was like:
"Okay, cool. Thanks, Winston."

So I add Winston.

Oh, but it still says
I have three friends, right,

because I have to go
and update this variable here.

That means, every time
that I add something to this array,

I have to update this variable,
and that could get really annoying,

especially if all of you guys
watching this

decide you'll be my friend.

And then, you know,
I'm updating this thousands of times

and having to update this every time.

So here's the thing:

We, so often, want to know
how long our array is,

that there's a special way to do that.

So the array will keep track
of how long it is

using a property called length.

And to use it, we just say,
myFriends.length,

and then we'll get back the length.

See, now it says 4,
and I can delete this variable.

I don't need it any more.

And this property will update
whenever we add.

So maybe OhNoes Guy!!
says he'll be my friend, and I'm like:

"Okay, you're kind of mean,
but okay, you'll be my friend."

And we can keep adding
and it'll keep updating.

So, that's really cool because, you know,

it's a lot less work to keep track
of how long our array is.

All right, so pretty much,

whenever you want to store
a list of values like this,

we'll use an array.

So keep watching to find out
all the really cool things

that we can use them for.