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In the English language,[br]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[br]these different parts of speech together.

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

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you'd be like,[br]"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[br]two nouns

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in front of an adjective,[br]in front of a verb.

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Doesn't work.

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But if I'd switched those and said,[br]"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,[br]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[br]my dog throwing a book.

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So in programming,[br]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[br]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[br]a number, and times when it doesn't.

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

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then whatever comes next[br]better be a number,

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

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

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

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

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

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And it's called Boolean

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because some dude[br]named George Boole invented it.

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And unlike a number[br]which has a ton of possible values,

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

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

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which means they're[br]super special awesome words.

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

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though you may not have realized it:[br]if statements!

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

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I'm just going to make a variable[br]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,[br]then I will draw this first ellipse."

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

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and indent it by selecting everything[br]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,[br]"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[br]that the top ellipse disappears.

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Alright, so this thing[br]inside the parentheses

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is actually a Boolean expression.

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Remember, a math expression[br]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[br]that evaluates to a Boolean.

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

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

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

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

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Yes, yes it is, and yes,[br]that is a Boolean expression.

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

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

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So back to our If statement.

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I can actually put anything[br]inside these parentheses,

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as long as it's a Boolean[br]or Boolean expression.

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

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

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

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

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which is kinda pointless,[br]the ellipse will always be drawn,

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

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

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so I'm going to make a new variable,[br]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[br]is definitely cool.

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And now that this variable[br]has a Boolean value,

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I can copy it and stick it[br]inside this If statement

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and now you can see the ellipse is drawn,

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because the value[br]of WinstonIsCool is true.

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I could also replace this[br]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[br]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[br]when the variable is true.

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

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

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

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Let's say I had a variable[br]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,[br]so that's a pretty bad variable name,

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

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

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

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

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Cool.

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Now let's look[br]at some other Boolean expressions.

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You've already seen[br]"less than" and "greater than",

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

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

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

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

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Indent that.

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And if you'd like to check if two things[br]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,[br]or "triple equals 48."

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

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except this time[br]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[br]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,[br]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,[br]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[br]the top-left ellipse is drawn.

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It's also greater than or equal to 48,[br]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[br]that bottom-right ellipse.

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And if we play around with number

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you can see it changes[br]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[br]can get really complicated.

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But we will talk about those another time.