WEBVTT

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In the English language,
we have different parts of speech,

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like noun, adjective, preposition, verb.

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And then there are a bunch of rules

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that tell us how to put
these different parts of speech together.

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So if I said something like,
"Dog books my eats,"

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you'd be like,
"What the heck does that mean?"

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And if you didn't realize this before,

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apparently, you can't just stick
two nouns

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in front of an adjective,
in front of a verb.

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Doesn't work.

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But if I'd switched those and said,
"My dog eats books,"

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then you would totally know what I meant.

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I could even replace this verb "eats"

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with another verb like,
I don't know, "throws",

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and it would still make grammatical sense,

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even if you can't imagine
my dog throwing a book.

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So in programming,
instead of parts of speech,

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we have these things called types.

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You've already seen one of these: numbers.

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We use numbers all the time
in our drawing code.

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And just like in English,

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there are times it makes sense to use
a number, and times when it doesn't.

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If I started typing in
this background function, "100 minus",

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then whatever comes next
better be a number,

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or at least something that evaluates
to a number like "14 + 15."

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On the other hand,
if I'd just typed "100 space",

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well, I can't really put
a number after that

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because "100-space-10"
doesn't mean anything.

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So there's another type in programming,
called the Boolean type.

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And it's called Boolean

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because some dude
named George Boole invented it.

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And unlike a number
which has a ton of possible values,

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a Boolean can only be
one of two values: true or false.

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And you can see
when I type them they turn blue,

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which means they're
super special awesome words.

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And you've already seen one place
where we use booleans,

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though you may not have realized it:
if statements!

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Let's get a quick refresh
on how those work.

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I'm just going to make a variable
called 'number, ' give it a number, 40.

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And write an If statement that says,

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"If number is less than 50,
then I will draw this first ellipse."

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I'm just going to copy this
into the If statement

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and indent it by selecting everything
and pressing tab.

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So now this statement says,

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"If number is less than 50," which it is,
"then we'll draw the top ellipse."

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And if I make number greater than 50,

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you can see
that the top ellipse disappears.

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Alright, so this thing
inside the parentheses

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is actually a Boolean expression.

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Remember, a math expression
is anything that evaluates to a number:

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like 3 plus 2 plus 4 times 8.

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So a Boolean expression is anything
that evaluates to a Boolean.

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A good way to check
if an expression evaluates to a Boolean,

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is to stick the word "is" in front of it,
and ask it like a question.

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If it sounds like a yes or no question,
then you know it's a Boolean expression.

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So here we can say,
"Is number less than 50?"

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Yes, yes it is, and yes,
that is a Boolean expression.

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On the other hand,
if I had something like, "4 + 4"

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and I tried to ask, "is 4 + 4?"
No. not a Boolean.

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So back to our If statement.

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I can actually put anything
inside these parentheses,

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as long as it's a Boolean
or Boolean expression.

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So I could say, "If true,"
and that ellipse would always be drawn.

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Or I could say, "If false,"
and the ellipse would never be drawn.

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I could also do something like
"If 3 is less than 4,"

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which is a Boolean expression
that will always evaluate to true,

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which is kinda pointless,
the ellipse will always be drawn,

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or "3 greater than 4,"
and that's always going to be false.

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And I can also assign Booleans
to variables, like this:

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so I'm going to make a new variable,
call it WinstonIsCool, and assign it

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a Boolean value, so true or false.

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Say true because Winston
is definitely cool.

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And now that this variable
has a Boolean value,

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I can copy it and stick it
inside this If statement

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and now you can see the ellipse is drawn,

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because the value
of WinstonIsCool is true.

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I could also replace this
with a Boolean expression,

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so could be "2 less than 4."

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Now if you're making a variable
that's meant for a Boolean value,

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you should give it a name

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that describes the condition
when the variable is true.

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A good way to check if you've picked
a good name for your variable

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is to put it in an If statement
and see if it makes sense as a condition.

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So, forget WinstonIsCool,
we already know that's true.

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Let's say I had a variable
called "muffins."

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All right, "If muffins." Hmm.

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Well, you know what?

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That doesn't tell me anything,
so that's a pretty bad variable name,

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but if I had "If muffinsAreBaking",
then that would tell me

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that when this variable is true,
then the muffins are baking.

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And don't ask me what muffins,
it's not important.

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So for now let's go back
to "If number is less than 50."

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Cool.

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Now let's look
at some other Boolean expressions.

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You've already seen
"less than" and "greater than",

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but you can also check
if something is "less than or equal to."

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So let's try, "If number is
less than or equal to 48."

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And we could also say, "If number
is greater than or equal to 48."

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If it is, we will draw
this top-right ellipse.

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Indent that.

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And if you'd like to check if two things
are exactly equal to each other

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or you could say: "If number"

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and then three equals signs,
or "triple equals 48."

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So that's a lot more like the equals sign
you're used to in math,

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except this time
you have three of them in a row.

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It's kind of overkill, right?

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And then finally, we have
if you want to check

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if two things are not equal to,

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so strictly not equal to, you can say,

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"If number" and then an exclamation point,
and then 2 equals signs, "48".

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And then we will draw that last ellipse.

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So if we go back to the top,
we can see that number is 48,

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so it is less than or equal to 48,

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which is why
the top-left ellipse is drawn.

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It's also greater than or equal to 48,
it's also equal to 48,

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but it is not not equal to 48,

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which is why we're missing
that bottom-right ellipse.

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And if we play around with number

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you can see it changes
which ellipses are drawn.

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So now you guys know about Booleans.

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And just like math expressions,

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Boolean expressions
can get really complicated.

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But we will talk about those another time.