Planning with pseudo-code | Intro to JS: Drawing & Animation | Computer Programming | Khan Academy

- When we write a program,
we are figuring out a way

to turn the brilliant ideas
in our head into actual code.

Here I want to talk about a technique

that many programmers use to do that

and it's what we call "pseudocode".

Now pseudocode is probably a
word you've never heard before

but basically, it's code
that looks a lot like English

or really, whatever language
you like to talk in.

Well, okay, that may not make sense

so let's talk through an actual example.

So let's say that I want to
draw a nice, symmetrical face.

So I might start by looking
at myself in the mirror

and maybe sketching it out

and seeing, okay well
I have this oval face,

I have two eyes and
they're about at this level

and this is where the
center of the face is

and now I have an idea for what
I want my face to look like.

So, I'll start writing it in pseudocode.

So let's see, the first
thing we want to do is

draw the face which is
an oval in the center.

Then we'd want to draw the two eyes,

which are two ovals, about
two thirds up the face

and maybe one fifth the size of the face.

Not exact math there, just
looking at my own face.

And then we draw the mouth which is a line

going halfway across the face

and maybe one third of the way up.

So, notice how I write
my pseudocode as comments

by starting each line
with the two slashes here.

That way I can write my
pseudocode in the program itself

and not have to worry about
getting any syntax errors

because the program will ignore comments.

Now that I've written this in pseudocode,

I can spend the time to turn each

of these lines of pseudocode
into actual bits of code.

Alright, so let's see.

For the face, an oval in the center.

Well that I'll use the
ellipse function for

and I'll figure out the
center of the screen here

and figure out a nice size.

Okay, that looks good.

For the eyes, once again
those are ellipses.

Everything on my face is
an ellipse, I'm very round.

It's going to be, let's
see, we'll do some math here

to get the eyes at a nice place

and make them about fit the size.

Okay, that looks good for the first eye,

I'll just copy and paste
to make the next eye.

Great.

Now, I can even leave my pseudocode

for a friend to implement
and they probably could

because I've given this
really nice description.

So I'm going to do that here
because we're friends, right?

So you might think this is silly,

why are we going through the effort

to write our program twice,
first in human language

and then in program language?

Well, this example was pretty simple

but pretty soon you'll be
building more complex programs

and it may be hard for you
to keep the whole program

in your head before coding it,

so what I usually do is
write the general idea

in pseudocode first and
then I'll spend more time

on the details of each part of that idea,

converting each line of
pseudocode into real code.

I think you'll find once
you start using pseudocode,

you'll do it more and more.

Try it in your next program and see.