Variables (6 mins)

In this section, I wanna add the idea of
variables to the code we have. So a

variable is like a box in memory. And that
box can store a value like a number or a

string or something. So, if you look
at this diagram here. If I have the line,

x=7. That's called a variable
assignment. And the way to think about

this is that in memory there's a box. So
I've drawn this little box here. And it's

labeled x. And it can hold a value. So
when the code says x=7, what

that means is pick up the value seven and
store that into the box. That is basically

what variable assignment does. So if I
look at this code example here that does

that. So in the first line I say x=7, so I'm storing a seven in

there, and then the later lines mention
x. This one says print(x) or print("lucky", x).

And those appearances of x, not with an
equal sign; those just retrieve the value

out of the box. So whatever was stored in
there, they're gonna use

that. So if I run this. Really what I get
is just, you know, the prints will end up

using seven. Because, this x=7
line stored a seven in the box, and the

subsequent lines just refer to x. If I
change this to eight, so I just change the

one line and I run it, okay well now, all
three lines refer to the eight, because

this line is storing an eight in the box.
Try one more experiment here; I guess

we've seen numbers and strings. Two data
types we can get pretty far with. So if I

say x="hi". This is
storing the string hi in the box. So if

I run that then I get, you know, these
lines will mention "hi". So in reality, this

name x - I chose x as my first example,
cause I feel that's a common variable in

math classes - but really this name, we
could sort of choose anything we wanted, so

if, just as long as we're consistent, so
I'm gonna change this to say xyz="hi",

so, that will create a variable
called xyz as for the "hi" in there and

then, all I need to do is make sure that
each one of these subsequent lines also

refers to xyz. So if I run it, this
program still works. So the gist of it is

that you can pick whatever name you want for the variable.

So long as, later on, when you wanna refer
to that variable, you use the same name.

You have to be consistent with yourself.
So the point of this sort of simple use of

variables kind of comes down to just,
saving repetition. It means that there's

some value that I want to use in my
program, I can assign it into a variable

on some early line, and then just use that
variable on a bunch of subsequent lines.

And if later I want to change the program
to use some other value, I can maybe just

change it in that one place, with the
variable. And then all the uses of that

variable will just use the new
value. And so actually we'll use that

pattern, for certain, pretty often in
our code. I should mention that this use

of the equal sign is not the same, as the
use of an equal sign in a math class or

an algebra class. In math, it is a stronger
statement if I say x=y. That's sort

of saying well these are equal all the
time. And in the computer, the equal sign

does not have that complicated of a
definition. Really, it's just assignment.

It's when this line runs; pick up whatever
this value is, and store it in the box

labeled, you know, xyz, or whatever.
So it just, it sort of happens when that

line runs. But it doesn't then have force
over the whole program. So it is

more simple than the use of equal sign
that you may be familiar with, from math

classes. Alright, so let me try. A little
code example that uses this, so, this

follows the pattern where it gives a little
output, and it says "right code, change the

code to produce this output". And so the
idea is that there was someone you had a

crush on, you know, in high school you
had a crush on someone and so we're gonna

write this little output about that. So
let's say, I had a crush on someone named

Alice. So then it's gonna say "Alice,
Alice, Alice, Alice", four times. And it

says, "In high school I had a crush on
Alice. Now the Alice curse is lifted." Now

the idea with this program is to not
repeat the name Alice a bunch of times. It

is to use variables, to, just have the
name once, so that if I decide instead I

had a crush on someone named Bob, or Zoe
or whatever. Then I can just change it in

the one place. So I'll say, x="Alice". This is what the problem statement

says. And the idea is to then write the
rest of the lines just referring to x. So,

in order to say the person's name four
times, I can just say print(x,x,x,x).

So let's just try
that. See and then I get four Alices. So

for the next line, it says "In high school
I had a crush on", and it's kinda like fill

in the blank right? I just want to use
whatever the name is. So I can do that by

saying print(", and this part just
doing as a string. So I'll just say. "In

high school I had a crush on", right that
part is all the same and then I'll end the

string and I'll say ,x). So it'll
print the string and then it'll follow it

with x. Let's just try. There we go. And
I'll do the last line. You'll notice the

semi-colons. I always put the semi-colons
in, in JavaScript and in reality they're

often optional. I'll say now the, this is
a little tricky so that's the string and

I'll say comma x. So again I sort of mix I
have the string and then x. So I get it up

here in the middle curse is lifted. Okay,
let's try that. There that works, so this

is a fairly simple use of variables where
we use an equal to a sign to it once and

maybe use it a few times below, but
actually that, that is the pattern we are

going to use in this class. I think you
are gonna like it a lot, so that's the

pattern I want you to practice.