Flowchart for the Factorial Program

Flowchart for the factorial program.

One thing you'll hear or see referred to a lot

is something called a flowchart

either in computer science,

so really when people talk about

any type of algorithm or process.

So what I thought I would do is

for every program I write—

is I'll do a simple flowchart.

Maybe I won't do it for every one,

but I'll start with some of the basic ones.

Just so we understand that

a flowchart really isn't anything fancy.

So in this factorial program

that we had been looking at

in the last couple of videos—

any flowchart you're just going to be a kind of starting point

which is really started, I guess,

depicted with a circle or an oval of some kind.

So we start, you can kind of view as

we starting at this line

above this assignment of the number

where we actually ask for input from the user.

And then, after that,

we ask for input from the user.

This line right here.

We are asking for input from the user.

So this right over here.

And we will depict that by a parallelogram.

So that is input from the user,

and then we could just say

"number equals user input".

And you can be a little bit loosey-goosey

with the terminology here,

you're really just trying to say

what you're doing in this step.

The parallelogram tells us that

we are somehow interfacing with the user.

We're either taking something from the user

or we're outputting something to the user.

So here, we're saying user input is equal to number.

We're assigning number as the user input.

Then, the next thing we do is just a straight up operation.

We just set product to be equal to 1, so we just set.

And there we just do that in a rectangle,

"product equals 1",

product is equal to 1.

And then, something interesting is going to happen.

We enter into our for loop.

And we start with—

and what I'm going to do here is

I'm going to write it a little bit different

than we wrote it over here—

so we do is we start a—

what we are doing is

we are going to start our for loop

essentially with an assignment

where we assign—

for loop is really a bunch of things

happening at the same time.

It assigns i to the first number in the sequence

or it tests whether it can assign i

to the first number in the sequence.

If it can,

then it proceeds.

If it can't,

then it breaks out of the for loop.

So let me put it this way.

I will do kind of a test case right over here.

So "items left in sequence".

And when I'm referring to the sequence

I'm talking about this sequence here—

the range of our number.

In the example I gave in the last video

the number was 3.

So items left in this sequence.

I know it's hard to read right over here.

If there are—so let's say that

there are items left in the sequence.

So if there are items left in the sequence.

So we'll just say

"i is equal to next item"

i is equal to next...

i is euqal to the next item.

If there are—

well, i'll just hold off for the case

where there are no items left in the sequence—

but let's say that there are.

"i is equal to the next item"

And then we also define—

we define product

to be

we define product

actually I want to do these in blue

just our regular...

Se let me write this

is "YES".

If there are items in the sequence,

then "i is equal to the next item"

that's one operation we do.

And then we reset product—

we reassign product to be equal to

what the former value of the product was

times i + 1.

And at this point, we essentially—

we loop back to this test over here.

So at this point, we loop back—

I'll try to write it neatly—

we loop back to—

let me do it right over here—

we loop back to this point in the program.

That's why it is called a loop.

Because after you perform this operation—

this is embedded in the loop—

you go back to the beginning

to see if there is any more of the loop to do.

So you go back to the beginning before the loop

and you say "Hey, are there any items in the sequence?"

and this should be a question mark over here.

This kind of question mark decision points

are usually specified with this diamond.

If there is another item in the sequence

then i is equal to the next item

and product is equal to

what product was times i + 1.

So we go to the next

"Are there items left in the sequence?"

And at some point

there won't be any items left in the sequence.

So there won't be—

at some point there won't be

any items left in the sequence.

And we could go to the right

or I'll just break out of it down here.

And now we've broken out of this for loop.

We've boken out of this for loop.

And then, the next thing we do

once we're done with our for loop

is we just print the value of product.

We just output the value of product.

So that is an interaction with the user.

So we are literally just outputting the value of product.

So we output—

"output product"

and we are done!

And I can write "end"

for the end of our program,

and the program will stop running.

"end".

So this is just a simple flowchart for this simple program.

And hopefully it helps you appreciate that

one little understanding of the program itself

if the last two videos didn't help too much,

and also gives you a simple understanding

of how to write a flowchart.