Additional Lecture: Variables

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En provenance du cours de University of London

Creative Programming for Digital Media & Mobile Apps

33 notes

University of London

Creative Programming for Digital Media & Mobile Apps

33 notes

This course is for anyone who would like to apply their technical skills to creative work ranging from video games to art installations to interactive music, and also for artists who would like to use programming in their artistic practice. This course will teach you how to develop and apply programming skills to creative work. This is an important skill within the development of creative mobile applications, digital music and video games. It will teach the technical skills needed to write software that make use of images, audio and graphics, and will concentrate on the application of these skills to creative projects. Additional resources will be provided for students with no programming background. At the end of this course, you will be able to: * Write creative, audiovisual programs in the Processing environment that run on desktop and mobile * Programatically manipulate sound in creative ways * Display images and image sequences * Generate interactive, algorithmic graphics * Work with a 2D physics engine to create a basic game

À partir de la leçon

Sonic Painter

This week we are getting up and running with the Processing IDE. We will show you the basics of writing Processing sketches then move onto some graphics and audio concepts. Mick will then introduce our first audiovisual example - SonicPainter, which allows users to interactively paint with synchronised graphics and sound.

Additional Lecture: Introduction To Programming 13:11

Additional Lecture: Variables 18:15

Rencontrer les enseignants

Dr Marco Gillies
Senior Lecturer
Computing Department, Goldsmiths, University of London
Dr Matthew Yee-King
Lecturer
Computing Department, Goldsmiths, University of London
Dr Mick Grierson
Reader
Computing Department, Goldsmiths, University of London

Welcome to the second lecture on introductory programming for those of you

doing the course we need for programming. So in this session I'd like to talk about

variables, but before we start let's have an example.

So let's write a simple processing program,

Correct the size of the screen, set as background, which I might if you haven't

looked at our main videos yet, you'll find out why number 255 is right in

there. And let's draw points, let's set stroke

rate say see the point and then draw, draw a point, position 100, 100 say.

That's a fairly basic processing program. And now we gave, it's just a point.

Where ever you want to draw a point in the middle of the screen.

Well, we can do something like this. The middle of the screen is half the

width and half the height, and we can do width divided by 2, height divided by 2.

And there we go to the point in the middle of the screen.

Now, what exactly have I done there? So we're quite used to, where the last

session we saw, we saw how we could call a command like point, using numbers.

But now we've used that's something different we've called point with width

divided by 2 height divided by 2. And so what is width?

It's a, it, behind the scenes, it's a number, a number that gives us the width

of the screen. And in the case of the example, it was

640. But here it's a name that stands for that

number, and I can use that name in the program Instead of using a number and I

can do calculations with it I've divided by 2.

That slash sign as we'll com to later is is division in the program, because we

don't have an easy like divide symbol in the, in the in the keyboard.

So That's a new element. And it's something that's called a

variable. A variable is essentially a name that can

stand for a number. It's called a variable because not only

can it stand for a number, it can change the number it stands for.

It can change. so what does that mean?

And what if we want to create own own variable?

And we'll see in future examples, it's very useful to have a, a name by which to

refer to a particular number. So, this is how we create a variable, and

I'll go through this in detail. If we're creating a known variable, it

will look something like this. we're correcting a variable that is a

number that starts off equal to 0. We first, we need to go back to our

example of what a computer is, you can think about what really is happening.

So this is our computer, it's got a processor and a memory, variables, astute

memory. And what happens?

What a variable is, is a little box in memory.

And, inside that little box of memory you can put memory or different things.

The first part of the of this command to, create a variable, int We'll come back to

exactly what that means but it's basically saying this is a number.

So create new box big enough to hold the number.

Next thing we do is give it a name. Call is pos X, for example.

That's just the name of the value. Call it anything, alright.

Call it John, call it Mark. In this example, I'm representing the X

position of something. So I'm going to call it posX.

And then we set it equal to a, to 0. That means we're putting in the number 0

inside our little box, in memory [INAUDIBLE].

So what we do in a case of variable is, a variable is basically a box in memory.

It has a name. And then can have values in.

those values can be numbers They can be other things.

So let's go back to what we were talking about in our.

Previous lecture about how memory is composed of a whole lot of 1s and 0s.

And think about 1s and 0s, what we said is that we can create lots of different

things after these 1s and 0s, interpret them in different ways.

So we could have basically true, false, very simple one bit.

There is [INAUDIBLE] one bit in reality but think of it as 1 bit.

You can have numbers as we saw we can have whole numbers, factional numbers, we

can have text, we can have really complex things like images and audio wave forms.

And each of these we can have variables to represent any of these things.

But the key thing is that they take different amounts of memory.

So a number, a whole number is actually [INAUDIBLE] different need from a

fractional number. And both of those things need a lot less

memory than text and certainly than an, than an image.

So when we're creating that little box in memory for a variable, we need to know

roughly how big it is and what kind of thing we're going to put in it.

And for that reason, we give names to all these different types of data.

And that this we call the different types, types and There's a tight Boolean,

which can be true or false, and that's it.

A tight int, that means integer, which is a mathematical word for whole number.

Float, a floating point number. Means a fractional number, sort of

decimal number. the reason it's called flight is slightly

complicated, but it's due to the representation of the number in the

computer. String is a word for a text, so it's this

little string of characters. And then there are complex types of

PImage and AudioBuffer that are specific to processing [UNKNOWN] Not, not yet.

Come back to those in a minute. We've also got a special type void.

Which we will come back to in a fu, future lecture, which represents nothing.

Come back to why we might want trips in life.

So that's, comes back to our little int in there.

That int And that posX represents the fact that posX is a number.

A whole number. So we can we know exactly what the

computer knows, exactly what kind of thing you want to put in.

That's why we can put zero in there, we can put a word like thread.

We can in turn say float instead of int and that will give us a factual number or

string if you want to put text in there. So, let's look at something else we might

do with the variable, setting its value. So this is saying that our variable when

setting in X position. Becomes equal to a number 34.

Now, let's just go back. Becomes equal to, that's an important

thing. Equal, those equal, that equal sign's, in

programming is what's called an assignment operator.

Takes one value on the left side of it, and sets it to be the new value.

So it changes the value of posX. It's not saying that they're equal to

begin with, but once you've done posX equals 34, after that posX is now 34.

That equal sign is how you change the values.

You can set a variable to equal to another variable.

So pos X is now going to have be equal to the width of the screen.

Or a function, certain functions do calculations and.

Can give you back numbers, or other values.

Up to now, the functions we've seen just do stuff like drawing.

But sometimes we have a function like random, a very useful function, which

generates a random number. So this call is going to give us a random

number between zero and 100. But he's going to set posX to be equal to

that random number. So after that posX is a random value.

And we'll see in the main lecture how we can use a number of these functions to do

calculations and then give us back a value that we put in the variable.

So we're giving numbers to, this random function, we're giving it zero and a 100.

That controls How it works. Basically, for say, 0 and 100, the

random, it will give us a number between 0 and 100.

If I say 0 and 10, it'll give us a number between 0 and 10, and then it gives us

back a number if you present posX to there.

Some functions return And return strings, texts, Boolean variable values, images,

it can return any kind of type, but something that we, can be put in a

variable. We can also do calculations and put the

results in a variable. So we can take a value, which in this

case. It is another there.

For mouseX. MouseX is a variable which represents the

position of the mouse. The X position of the mouse.

And we add something to it. We add 1.

That gives us a new number. Whatever mouse X is plus 1 set for mouse

X. It's 100.

It's 101 If you can do basic math. And we take that value and put it in

posX. .

and we can do something else. We can take the value and change it based

on it's own old value. So we can take posX, make it equal to.

Itself but the old value of posX plus 1. So if posX is 30, we add 1 to 31 and set

posX to that. That's a way of changing a variable as we

use it. in in future lessons we'll see how we can

use that to animate things. By every time changing the value of the

variable, if that position, variable is a position or something similar, we can

make things move around. This is such a common thing to do,

there's this little shorthand for it. PosX plus equals one means posX equals

posX plus 1. It means exactly the same thing.

It's a way of adding a value to itself. posX plus, plus is an even shorter

shorthand when the, you know the value of adding is 1.

posX plus, plus just means add one. PosX.

PosX plus equals means add a number to it.

All these three expressions are showing you, these three lines of code, are the

exact same thing. But in the first two, I could change the

value of 1 and add 2 instead. The last one is always been adding 1.

So, let's look at some of the, things you can do with calculations.

You can do some basic maths. We've seen how to add; you use the plus

sign. Straightforwardly, to add two things

you'd do plus equals. If you want to add something to a

variable And plus, plus if you want to add one to a variable, could do exactly

the same with subtract, minus signs, take two numbers and subtract them, minus

equals subtract number from a variable, minus, minus, subtract one.

Star is asterisk, is used for multiplication, because there's no sort

of multiply sign on the standard keyboard.

And we can do star equals to multiply the value of err by something that no

equivalent to plus, plus. The slash is the divide symbol, star's

the multiply. So those are some basic math, there're

more operations. That's it for now.

another thing you need to think about in terms of calculations is brackets.

If you want to do multiple calculations on one line and combine them together,

you can put brackets 'round them as you would in standard maths to constrain

which happens first. So, this stuff in the inner brackets is

done first. You calculate the first brackets, and

then use the results of that calculation in the outer brackets.

So you'll, what's happening here is you're multiplying x by 3 and you're

adding 1 to the result. Okay, so let's get back to various types.

We've talked a lot about Variables now and how we can have different types of

boolean, int, float, string. it mostly talked about numbers because

that's mostly what we're going to be using in graphics.

In the future we will talk about boolean. But now I want to talk basically about

things like PImage and AudioPlayer, because they're actually much more

complex than something like a number. Obviously a, a whole audio file is more

complex than a number, but even the way the variable works is slightly different.

So this week Matthew's going to talk about AudioPlayer; let's have a look at

it. So just as we did int pause x, we get the

type of the variable and the name. Here we give the title variable audio

player, and the name, is player. You can give it any name you like.

if it's a high hat we can call it high hat, if it's a violin sound we can call

it violin. We can call it anything we like.

so that's essentially the same thing. and Minim is another aud type we use in

audio. Matthew will talk about exactly what all

that's used for, but here is how we create Minim objects.

So, just as we set the value. Of our int variable to 0.

You can set the value of an object, and so I didn't use the term, but these

complex types are called objects. Our object's called Minim.

Now, we need an extra bit in here, because there's no easy way of saying

Right? We can just write three, if you want a

new variable, a new number. But there's no quite so easy way of doing

that. We need a new command called new, and

what new does is create a new object. And it does it by calling a function.

Called a constructor. This is like a command but it has the

same name as the type, as the object. And it's used to create any value of

those objects. They're new in the constructor.

By the name of the type combine together to create a new value of the objects.

And you can [INAUDIBLE] pass parameters in just like any other command.

Matthew will explain this, but this essentially means, the, it's something

that wraps into programming, you don't have to worry about it too much.

But it's an example of passing something in, so that can be used in creating an

object. So, In an audio file, you might pass in

the file name. In an image, you might pass in how, the

width and height of the image. There's lots of things you could pass.

And then there's another important thing, big difference between types like numbers

and objects. A number Is just a number you can do some

calculations on. In a, in an object, as well as having its

value, you can call a function on that object.

What that means is, if you're calling a function play, but that's not a generic

function, that doesn't apply everywhere, you know, you can't just play.

You're playing a particular audio file. 'Kay, meaning to play an audio file.

And that's why we do this little bit of style of code where we're doing

player.play. Recalling play On a specific object.

[INAUDIBLE] specific audio file, not general audio file just one particular

item. And we're using this little dot.

What a dot does is links the function you're calling to things have been

called. So you do, player.play Cause of function

one specific object. A very useful capability.

So this is something that Mathew's going to use and that Nick and I are

going to use in the examples a bit later in this lesson.

So that was a very brief introduction to variables.

You'll see a lot of examples in the main lessons.

And and hopefully that will help you understand these concepts that we build

on programming. If you need some more help we've provided

a bunch of links relating to programming on the main site.

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