Software Engineering: Crash Course Computer Science #16 CrashCourse English English (auto-generated)

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Hi, I’m Carrie Anne, and welcome to CrashCourse Computer Science!

hi I'm Kerry Ann and welcome to crash

So we’ve talked a lot about sorting in this series and often code to sort a list of numbers

course computer science so we've talked a lot about sorting in this series and often code for sorting lists of numbers

might only be ten lines long, which is easy enough for a single programmer to write.

is only ten lines long which is pretty easy for a single programmer to write

Plus, it’s short enough that you don’t need any special tools – you could do it

plus it's short enough that you don't need any special tools you can do it in

in Notepad. Really!

notepad really but a sorting algorithm

But, a sorting algorithm isn’t a program; it’s likely only a small part of a much

isn't a program it's likely only a small

larger program.

part of a much larger program for

For example, Microsoft Office has roughly 40 millions lines of code.

example Microsoft Office has roughly 14

million lines of code 14 million that's

That’s way too big for any one person to figure out and write!

way too big for any one person to figure

To build huge programs like this, programmers use a set of tools and practices.

out right to build huge programs like this programmers use a set of tools and

Taken together, these form the discipline of Software Engineering – a term coined

practices taken together these form the discipline of software engineering a

by engineer Margaret Hamilton, who helped NASA prevent serious problems during the Apollo

term coined by engineer Margaret Hamilton who helped NASA prevent serious

missions to the moon.

problems on the Apollo 11 mission to the

She once explained it this way: “It’s kind of like a root canal: you waited till

moon she once explained it this way it's kind of like a root canal you waited till the

the end, [but] there are things you could have done beforehand.

end but there are things you could have

It’s like preventative healthcare, but it’s preventative software.”

done beforehand it's like preventative health care but

it's preventative software

As I mentioned in episode 12, breaking big programs into smaller functions allows many

as I mentioned in episode 12 breaking big programs into smaller functions

people to work simultaneously.

allows many people to work

They don’t have to worry about the whole thing, just the function they’re working on.

simultaneously they don't have to worry about the whole thing just the function

So, if you’re tasked with writing a sort algorithm, you only need to make sure it sorts

they're working on so if your task of writing a sort algorithm you only need

properly and efficiently.

to make sure it sorts properly and

However, even packing code up into functions isn’t enough.

efficiently however even packing up code into functions isn't enough Microsoft

Microsoft Office probably contains hundreds of thousands of them.

Office probably contains hundreds of

That’s better than dealing with 40 million lines of code, but it’s still way too many

thousands of them that's better than dealing with 40 million lines of code but there's still way too many things

“things” for one person or team to manage.

for one person or team to manage the

The solution is to package functions into hierarchies, pulling related code together

solution is to package functions into hierarchies pulling related code

into “objects”.

together into objects for example cars

For example, car’s software might have several functions related to cruise control, like

software might have several functions related to cruise control like setting

setting speed, nudging speed up or down, and stopping cruise control altogether.

speed nudging speed up or down and stock

Since they’re all related, we can wrap them up into a unified cruise control object.

in cruise control altogether since they are all related we can wrap them up into a unified cruise control object but we

But, we don’t have to stop there, cruise control is just one part of the engine’s

don't have to stop there cruise control is just one part of the engine software

there might also be sets of functions

There might also be sets of functions that control spark plug ignition, fuel pumps, and

that control spark plug ignition fuel

pumps and the radiator so we can create

So we can create a “parent” Engine Object that contains all of these “children”

a parent engine object that contains all

of these children objects in addition to

In addition to children *objects*, the engine itself might have its *own* functions.

children objects the engine itself might

You want to be able to stop and start it, for example.

have its own functions you want to be able to stop and start it for example it

It’ll also have its own variables, like how many miles the car has traveled.

will also have its own variables like how many miles the car has traveled in

In general, objects can contain other objects, functions and variables.

general objects can contain other objects functions and variables and of

And of course, the engine is just one part of a Car Object.

course the engine is does one part of a

There’s also the transmission, wheels, doors, windows, and so on.

car object there's also the transmission wheel stores windows and so on now as a

Now, as a programmer, if I want to set the cruise control, I navigate down the object

programmer if I want to set the cruise control i navigate down the object

hierarchy, from the outermost objects to more and more deeply nested ones.

hierarchy from the outermost objects to more and more deeply nested ones

Eventually, I reach the function I want to trigger: “Car, then engine, then cruise

eventually I reach the function I want to trigger car then engine then cruise

control, then set cruise speed to 55”.

control then set cruise speeds 55

Programming languages often use something equivalent to the syntax shown here.

programming languages often use something equivalent to the syntax shown

The idea of packing up functional units into nested objects is called Object Oriented Programming.

here the idea of packing up functional units and nested objects is called object-oriented programming this is very

This is very similar to what we’ve done all series long: hide complexity by encapsulating

similar to what we've done all series long hide complexity by encapsulating

low-level details in higher-order components.

low-level details in higher-order

Before we packed up things like transistor circuits into higher-level boolean gates.

components before we packs up things like transistor circuits into higher-level boolean gates now we're

Now we’re doing the same thing with software.

doing the same thing with software yet

Yet again, it’s a way to move up a new level of abstraction!

again it's a way to move up a new level of abstraction

Breaking up a big program, like a car’s software, into functional units is perfect

breaking up a big program like a car software into functional units is

perfect for teams one team might be

One team might be responsible for the cruise control system, and a single programmer on

responsible for the cruise control system and a single programmer on that

that team tackles a handful of functions.

team tackles a hand for the function

This is similar to how big, physical things are built, like skyscrapers.

this is similar to how big physical

You’ll have electricians running wires, plumbers fitting pipes, welders welding, painters

things are built like skyscrapers you'll have electricians running wires plumbers fitting pipes world of welding painters

painting, and hundreds of other people teeming all over the hull.

painting and hundreds of other people teaming all over the whole they work

They work together on different parts simultaneously, leveraging their different skills.

together on different parts simultaneously leveraging their

Until one day, you’ve got a whole working building!

different skills until one day you've got a whole working building but

But, returning to our cruise control example… its code is going to have to make use of functions

returning to our cruise control example its code is going to have to make use of

in other parts of the engine’s software, to, you know, keep the car at a constant speed.

functions in other parts of the engine software to you know keep the car at

That code isn’t part of the cruise control team’s responsibility.

constant speed thank code is in part for cruise control

It’s another team’s code.

teams responsibility it's another team's

Because the cruise control team didn’t write that, they’re going to need good documentation

code because the cruise control team didn't like that they're going to need

about what each function in the code does, and a well-defined Application Programming

good documentation about what each function in the code does and a well-defined application programming

Interface -- or API for short.

interface or API for sure you can think

You can think of an API as the way that collaborating programmers interact across various parts

of an API as the way that collaborating programmers interact across various

parts of the code for example in the

For example, in the IgnitionControl object, there might be functions to set the RPM of

ignition control objects there might be functions to set the RPM of the engine

the engine, check the spark plug voltage, as well as fire the individual spark plugs.

check the spark plug voltage as well as

Being able to set the motor’s RPM is really useful, the cruise control team is going to

fire the individual spark plugs being able to set the motors RPM is really useful the cruise control team is going

need to call that function.

to need to call that function but they

But, they don’t know much about how the ignition system works.

don't know much about how the ignition

It’s not a good idea to let them call functions that fire the individual spark plugs.

system works it's not a good idea to let them call functions that fire the

Or the engine might explode!

individual spark plugs on the engine

might explode maybe the API allows the

The API allows the right people access to the right functions and data.

right people access to the right

Object Oriented Programming languages do this by letting you specify whether functions are

functions and data object-oriented programming languages do this by letting

public or private.

you specify whether functions are public

If a function is marked as “private”, it means only functions inside that object

or private if a function is marked as private it means only functions inside

that object can call it so in this

So, in this example, only other functions inside of IgnitionControl, like the setRPM

example only other functions inside of ignition control like the set rpm

function, can fire the sparkplugs.

function can fire the spark plug on the

On the other hand, because the setRPM function is marked as public, other objects can call

other hand because the set rpm function is marked of public other objects can

it, like cruise control.

call it like cruise control this ability

This ability to hide complexity, and selectively reveal it, is the essence of Object Oriented

to hide complexity and selectively reveal it is the essence of

Programming, and it’s a powerful and popular way to tackle building large and complex programs.

object-oriented programming and it's a powerful and popular way to tackle building large and complex programs

Pretty much every piece of software on your computer, or game running on your console,

pretty much every piece of software on your computer or game running on your

was built using an Object Oriented Programming Language, like C++, C# or Objective-C. Other

console was built using an object-oriented programming language like C++ C sharp or Objective C other

popular “OO” languages you may have heard of are Python and Java.

popular aro languages you may have heard

It’s important to remember that code, before being compiled, is just text.

of a Python and Java it's simple remember that code before being compiled

As I mentioned earlier, you could write code in Notepad or any old word processor.

is just text and I mentioned earlier you could write code in notepad or any old

Some people do.

word processor some people do but

But generally, today’s software developers use special-purpose applications for writing

generally today's software developers use special-purpose applications for

programs, ones that integrate many useful tools for writing, organizing, compiling and

writing programs ones that integrate many useful tools for writing organizing

compiling and testing code because

Because they put everything you need in one place, they’re called Integrated Development

there's put everything you need in one place they're called integrated development

Environments, or IDEs for short.

environment or IDE is for sure all ideas

All IDEs provide a text editor for writing code, often with useful features like automatic

provide a text editor for writing code often reviews for features like

color-coding to improve readability.

automatic color coding to improve

Many even check for syntax errors as you type, like spell check for code.

readability many even check the syntax errors as you type like spell check for

Big programs contain lots of individual source files, so IDEs allow programmers to organize

code big programs contain lots of individual source files so either use

and efficiently navigate everything.

allow programmers to organize and efficiently navigate everything also

Also built right into the IDE is the ability to compile and run code.

built right into the IDE is the ability to compile and run code and if your

And if your program crashes, because it’s still a work in progress, the IDE can take

program crashes because it's still a work in progress

you back to the line of code where it happened, and often provide additional information to

the IDE you can take you back from the line of code where it happened and often

help you track down and fix the bug, which is a process called debugging.

provide your additional information to help you track down and fix the bug which is a process called debugging this

This is important because most programmers spend 70 to 80% of their time testing and

is important because most programmers spend 70 to 80 percent of their time

debugging, not writing new code.

testing and debugging not writing new

Good tools, contained in IDEs, can go a long way when it comes to helping programmers prevent

code good tools contained in ideas can go a long way when it comes to helping

and find errors.

programmers prevent and find errors many

Many computer programmers can be pretty loyal to their IDEs though - but let’s be honest.

computer programmers can be pretty loyal to their ideas though but let's be

VIM is where it’s at.

honest BIM is where it's at providing

Providing you know how to quit.

you know how to quit in addition to

In addition to coding and debugging, another important part of a programmer's job is documenting

coding and debugging another important part of a programmers job is documenting

their code this can be done in

This can be done in standalone files called “read-me’s” which tell other programmers

standalone files called read needs which

to read that help file before diving in.

tell other programmers to read that help

It can also happen right in the code itself with comments.

file before diving in it can also happen right in the code itself with comments

These are specially-marked statements that the program knows to ignore when the code

these are specially marked statements that the program knows to ignore when

the code is compiled they exist own to

They exist only to help programmers figure out what’s what in the source code.

help programmers figure out what's what

Good documentation helps programmers when they revisit code they haven’t seen for

in the source code good documentation helps programmers when they revisit code

awhile, but it’s also crucial for programmers who are totally new to it.

they haven't seen for a while but it's also crucial for programmers who are

I just want to take a second here and reiterate that it’s THE WORST when someone parachutes

totally new to it I just want to take a second here and reiterate that it's the worst when someone parachutes our mode

a load of uncommented and undocumented code into your lap, and you literally have to go

of uncommented an undocumented code ensure that and you literally have to go

line by line to understand what the code is doing.

line by line to answer that what the

code is doing seriously don't be that

Don’t be that person.

Documentation also promotes code reuse.

documentation also promotes code reuse

So, instead of having programmers constantly write the same things over and over, they

so instead of having programmers constantly write the same things over

can track down someone else’s code that does what they need.

and over they can track down someone else's code that does what they need

Then, thanks to documentation, they can put it to work in their program, without ever

then thanks to documentation they can put it to work in their program without

having to read through the code.

ever having to read through the code

“Read the docs” as they say.

read the docs as they say in addition to

In addition to IDEs, another important piece of software that helps big teams work collaboratively

ID is another important piece of software that helps

on big coding projects is called Source Control, also known as version control or revision control.

dick teams work collaboratively on big coding projects is called source control also known as version control or

Most often, at a big software company like Apple or Microsoft, code for projects is stored

revision control most often a big software company like Apple or Microsoft code for projects installed on

on centralized servers, called a code repository.

centralized servers called a code

When a programmer wants to work on a piece of code, they can check it out, sort of like

repository when a programmer wants to work on a piece of code they can check

checking out a book out from a library.

it out so I was like checking out a book

Often, this can be done right in an IDE.

from a library often this can be done

Then, they can edit this code all they want on their personal computer, adding new features

right in an IDE then they can edit this code all they want on their personal computer adding

and testing if they work.

new features and testing if they work

When the programmer is confident their changes are working and there are no loose ends, they

when the programmer is confident their changes are working and there are no

can check the code back into the repository, known as committing code, for everyone else

loose ends they can check the code back into the repository known as committing

code for everyone else to use while a

While a piece of code is checked out, and presumably getting updated or modified, other

piece of code is checked out and presumably getting updated or modified

programmers leave it alone.

other programmers leave it alone this

This prevents weird conflicts and duplicated work.

prevents weird conflicts and duplicated

In this way, hundreds of programmers can be simultaneously checking in and out pieces

work in this way hundreds of programmers can be simultaneously checking in and

of code, iteratively building up huge systems.

out different pieces of code it's relatively building up huge systems

Critically, you don’t want someone committing buggy code, because other people and teams

critically you don't want someone committing buggy code because other

may rely on it.

people and teams may rely on it their

Their code could crash, creating confusion and lost time.

code could crash creating confusion and

The master version of the code, stored on the server, should always compile without

lost time the master version of the code stored on the server should always

errors and run with minimal bugs.

compile without errors and run with

But sometimes bugs creep in.

minimal bugs but sometimes bugs do creep

Fortunately, source control software keeps track of all changes, and if a bug is found,

in fortunately source control software keeps track of all changes and if a bug

the whole code, or just a piece, can be rolled back to an earlier, stable version.

is found the whole code or just a piece can be rolled back to the earlier stable

It also keeps track of who made each change, so coworkers can send nasty, I mean, helpful

version it also keeps track of who made each change so coworkers can say nasty I mean

and encouraging emails to the offending person.

helpful and encouraging emails to the

Debugging goes hand in hand with writing code, and it’s most often done by an individual

offending person debugging goes hand-in-hand with writing code and it's

most often done by an individual or

The big picture version of debugging is Quality Assurance testing, or QA.

small team the big picture version of debugging is quality assurance testing

This is where a team rigorously tests out a piece of software, attempting to create

or QA this is where a team rigorously test out a piece of software attempting

unforeseen conditions that might trip it up.

to create unforeseen conditions that

Basically, they elicit bugs.

might trip it up basically they

Getting all the wrinkles out is a huge effort, but vital in making sure the software works

intercept bugs getting all the wrinkles out is a huge effort but vital in making

as intended for as many users in as many situations as imaginable before it ships.

sure the software works as intended for as many users in as many situations as imaginable before it ships you've

You’ve probably heard of beta software This is a version of software that’s mostly complete,

probably heard of base of software this is a version of software that's mostly

but not 100% fully tested.

complete the nine hundred percent fully

Companies will sometimes release beta versions to the public to help them identify issues,

tested companies will sometimes release base versions to the public to help them

it’s essentially like getting a free QA team.

identify issues it's essentially like getting a free QA team what you don't

What you don’t hear about as much is the version that comes before the beta: the alpha version.

hear about as much is the version that comes before the beta the alpha version

This is usually so rough and buggy, it’s only tested internally.

this is usually so rough and buggies

So, that’s the tip of the iceberg in terms of the tools, tricks and techniques that allow

only tested internally so that's the tip of the iceberg in terms of the tools

software engineers to construct the huge pieces of software that we know and love today, like

tricks and techniques that allow software engineers to construct the huge pieces of software that we know enough today like YouTube Grand

YouTube, Grand Theft Auto 5, and Powerpoint.

Theft Auto 5 and PowerPoint as you might

As you might expect, all those millions of lines of code needs some serious processing

expect all those millions of lines of code need some serious processing power

power to run at useful speeds, so next episode we’ll be talking about how computers got so incredibly fast.

to run it useful speeds so next episode we'll be talking about how computers got so incredibly fast see you then crash

course computer science is produced in association with PBS Digital Studios at their channel you can check out a playlist of shows like physics gold deep

look at PBS space types this episode will films at the chad and stacy ever got studio in indianapolis indiana and it was made with the help of all these

nice people and our wonderful graphics team is thought cafe that's where we're going to have to halt and catch fire see you next week

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