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2D Arrays

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Introduction To Swift Programming

University of Toronto

3.9 (1,247 ratings) | 55K Students Enrolled

Course 1 of 4 in the iOS App Development with Swift Specialization

Introduction to Swift Programming is the first course in a four part specialization series that will provide you with the tools and skills necessary to develop an iOS App from scratch. By the end of this first course you will be able to demonstrate intermediate application of programming in Swift, the powerful new programming language for iOS. Guided by best practices you will become proficient with syntax, object oriented principles, memory management, functional concepts and more in programming with Swift. This course is unique in its dedication to teaching Swift programming. With new features and capabilities you will be at the forefront of writing iOS apps. Currently this course is taught using Swift 2. The team is aware of the release of Swift 3 and will be making edits to the course in time. Please be aware that at this time the instruction is entirely with Swift 2. Please note that to take part in this course (and the full specialization) it is required to have a Mac computer and, though not required, ideally an iPhone, iPod, or an iPad. NOTE: This course has been designed and tested (and content delivered) on a Mac. While we are aware of hacks and workarounds for running Mac in a virtual machine on windows we do not recommended a PC. We hope you have fun on this new adventure.

Skills You'll Learn

iOS App Development, Syntax, Computer Programming, Swift (Programming Language)

Reviews

3.9 (1,247 ratings)

5 stars
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4 stars
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1 star
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LO

Jul 29, 2016

Amazing course with awesome material.\n\nA great way to start learning the basics of Swift and getting to know people that have the same aspiration of learning new stuff.

AC

Jun 25, 2016

It's very easy. On the other hand the teachers do not do very deep and you need to do a lot of selfstudy. Would not recommend for the ones without basic knowledge of CS.

From the lesson

Swift Basics

In this module we will introduce the basic concepts of Swift. To begin you will learn variable declaration, different types, and program control mechanisms. Here we start to build the foundation of iOS app development with Swift. We hope you enjoy the journey.

Introduction to the Module0:37

Setting Up Playground7:17

Simple Control Flow9:50

Arrays and Dictionaries7:28

Taught By

Parham Aarabi
Professor

Transcript

[MUSIC]

Hello, in this lecture, we're gonna summarize everything we've learned so

far and introduce you to some image processing on the most basic level using

what we've learned so far.

And this should be very helpful with the final project of this course.

And so, this will be your first look at sort of what kind of things we'll be doing

throughout this course, and further on in specialization.

All right, so we've learned a few things so far.

We're gonna start by defining a 2D array that

represents an image, so let's do that, image =,

and then sort of open up with some new lines here.

And within an image are pixels, and

pixels are generally represented just by integer values.

And so, we're gonna simplify every down and

say that images are just 2D arrays of numbers from 0 to 10.

So we've got this image, it looks like this.

As you can see, I'm sort of painting before your eyes.

Yeah, that's nice.

Let's add an 8.

Beautiful.

And even a 2.

All right, so here's our image, and this actually, albeit very simple,

it's a good representation of an image because, if it was a three-pixel image,

here you would have brightness, and you would be able to see something.

It's a bit of a stretch, but we're gonna keep calling an image,

and we're going to define a function that processes this image in a certain way.

And so, if you recall, func, and

what we're gonna do is, we're gonna take these sort of darker parts,

if we say that the lower numbers are sort of darker parts of the image, and

just make them brighter cuz darkness doesn't look as good.

All right, so we're gonna call it raiseLowerValuesOfImage.

I'm gonna pass an image, and we have to give it its type.

Do you remember it?

The type of a 2D array is simply an array of int.

And if you ever are not sure what to put here, you can hold Alt and

click on this, and it will give you the type, and this is shorthand,

so the square brackets like this are shorthand for array.

With the angle bracket bit type, so this looks much nicer.

All right, and soon we're gonna see something interesting about this

definition that we've never seen before, but first let's do some processing.

All we're gonna do is take any lower value, say less than 5, and

set it equal to 5, so we'll have a double for loop.

Remember we can do a for in loop here,

as in for, we're going to call this a row cuz we're gonna get a row for

the first iteration in image.

Remember, what's a row?

So a row will be a single array of integers now.

That's exactly what you want, and now we go to the columns.

In each row, and a column should be an integer.

Great, now we get the value here, and although this is nice and it's great for

reading the value, the interesting thing is we can't really set the value here.

Because we have image, but

we don't know which pixel we're on, so we're going to do this differently.

I just wanted to show you this.

All right, so we're going to have to know which exact coordinate we're on,

like (0,0), (0,1), so forth.

So we're gonna have an i.

We're actually gonna use row, but instead of in the image,

we're gonna make it be an integer, so we can go from 0 to image.count,

and so we use the range operator as we've seen once before.

And now row is directly an integer.

It's similar to before but different, as in now in this next column,

we are going to have to access the actual row image.

We can still call .count because image, once you access the row,

it's a single array, and now in columns and other count from 0 to the length,

which in this case is 3, so what can we do here?

Here we know that we can read the value of the pixel, which is just image row column,

and if we call this right now, raiseLowerValuesOfImage,

it should run nine times and tell us what it printed,

and we can see that again from here.

And it tries to graph it to us cuz it is called sequentially, and you see it's 3,

7, 10, 6, 4, 2, etc.

I'm going to hide that.

All right, so this works, we want to set it to something, so

we need an if statement here.

So if this value is less than 5, we're simply gonna set it to 5,

and this is where we're going to get an error.

And we're going to read the error, and it is,

we cannot assign it because image is a constant.

When you pass a parameter into a function you can't modify that parameter.

That's what return values are for, but in cases like this,

where you do want to modify the parameter, you can mark it with var, and

there's a nice fix it here which makes it super easy.

Let's just click on that, and all it did was add var to our parameter, and

now it works.

And now we raise the value of our image.

We're still calling it, and

it says it ran four times, which would be one, two, three, four.

Four times is correct, and now if we print out imaging in down here, all right,

so once we print out image, we see our function's not working as intended.

And this is great, well, this is not great, but now this lets

me demonstrate something more to you, and I do know why that's the case.

So, when you set it as var,

it's still passing in a copy of the image because image is a structure.

You get a copy of the image inside your function.

When you set it to a var, it becomes mutable so

you can change it as much as you want into function, but

it's not actually changing this image outside of the function that we passed in.

So, if you print this image here, you'll see that it hasn't even been changed, but

it hasn't been changed here.

And so, can we get what we want, though?

Can we actually change image?

We can, and it's a different sort of modifier here.

Var means that to pass it in and create a variable that you can change, but

there's another parameter called inout, which is what we want,

which means it comes in and it goes out.

That's how I see it, but what it means is that now it's almost passed by reference.

Now you're passing this by reference, and

when you do changes to it, they will be reflected outside, too.

And inout is a bit special, as you can see, we get an error down here to make it

clear when you're calling the function that this parameter might be changed.

Swift makes you add an ampersand to it.

This is a lot like passing a reference in C and

C++, and it's really nice, so when you do this, you know that it might be changed.

And when you don't do this,

you know that your variable will not be touched by this function.

All right, now that we've made this change, we can see image has,

indeed, now been modified by this function.

And so, yes, this is a good overview of what we learned so far, and

I hope this helps you later on in your assignments.

We'll see you next lecture.

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