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January 18, 2015
LEARN
to code
IN
STNMAST2008
1
day
MAKE YOUR
OWN APP:
part one
CREATE AN APP IN A DAY
If you can’t code,
you’ll be left in the
past — so snap to it
Coding is no longer a geeks’ hobby: it’s everywhere. Now is the time for
families to hone their HTML, crack CSS and jump into JavaScript together, and
our hi-tech snap app is a brilliant way to get started, writes Kathryn Parsons
W
hether you are 60 or six years
old, understanding the technology behind
the screen is becoming increasingly valuable.
In today’s world digital literacy and
programming skills are in high demand and
short supply across every industry and sector.
By taking your first steps behind the screen,
you may unearth a latent talent and love of
programming or at the very least begin to
understand the machines influencing our
lives. An exciting journey lies before you.
Only a tiny percentage of the world is
code-literate, but coding is one of the most
creative skills that anyone could have — and
this is what we’ve set out to prove in our
Learn to Code guide over the next two weeks.
More than 12,000 of you took your first steps
into the world of programming in September
last year, coding your very own quiz game
app. This week and next we bring you another
tutorial in our Learn to Code series, using the
Playto online code education platform
designed by the team at Decoded.
We’ll be teaching you to code your own web
app called Snap That! (well, that’s what we’ve
called ours — you can give yours any name
you like). It’s a game of snap that you can
code, customise and then play with friends or
family on your smartphone or tablet.
Snap That! will introduce you to algorithms
— using logical reasoning to design computer
programs that make decisions — while guiding
you through the creating and debugging
process. Not only is this valuable and fun for
adults; we’ve also taken care to ensure the
tutorials cover the key aspects of the new
computing curriculum for key stages 1 and 2
— so you and your kids can learn together.
Apply your problem-solving skills,
creativity, persistence and imagination to the
task at hand. You are about to go further
behind the screen than a vast proportion of
the web-consuming population has ever been.
You are about to become a creator of
something that could be as simple and fun as a
game or could inspire a business idea or help
formulate new ideas in your job — the
possibilities of code are truly endless.
The future is being written in lines of code.
Become part of that future.
Everyone loves the card game
snap. We’re going to build a
touchscreen version
1
THE BRIEF
1
The Playto Editor
Introduction to our editor environment
Wireframing
If you fail to plan, plan to fail
3
Coding our content
First bits of content using HTML
Kathryn Parsons, chief executive of Decoded
Since the start of this school year coding has been part of the
national curriculum, so there’s never been a better time for
families to get coding together. Don’t worry if this tutorial
challenges you: it’s the equivalent of finishing key stage 2
!
2
“You are about to go further
behind the screen than most of
the population has been. The
future is being written in lines of
code. Be part of that future”
STNMAST2008
4
Valid HTML
Following the rules of html to make our
content ‘valid’
5
Meta and Structural HTML
Giving our app shape and description
6
Intro to CSS
Connecting our stylesheet to do some design
7
Designing our User Interface
Getting creative with CSS
8
choosing images
Finding pictures for the game to use
9
programming overview
The three key ideas behind computer languages
10
intro to javascript
We will start by
“wireframing”, or
planning, the app.
We’ll then work on
defining the content
and setting up our
page. With our basic
content in place, we can focus on the design of our app.
Once it looks right, we can begin to make it work.
The Playto Editor
On any computer, start by going to:
thesundaytimes.co.uk/learntocode.
Sign in to the Playto Editor (you’ll need to sign up first if you
haven’t before), and then start following the instructions
below. As you create your app, the editor will automatically
save your work and update a preview to give you feedback as
you progress. But first we need to do some planning.
2
Wireframing
12
Random Image
Selecting a random image
absolutely vital to building an
app. If you sit down and start
sketching, it’s possible to
explore multiple options for
what your app could do and
how it could look.
the Google Docs Draw app, with a template of app
wireframes — go to tinyurl.com/nun28lr. We want to include
the title of our app, a button to start the game, space for two
images to display and a space to show the player scores.
Carrier
12:00
Snap That
PLAY
Player 1:0
Player 2:0
Carrier
This is looking
a little busy. We
could hide the
player scores
until play begins.
This gives us
space to put the
images stacked
on top of each
other ...
12:00
Snap That
PLAY
Better. But we could
make things even
neater by combining
the title with the play
button, and move it
between the images to
balance the layout ...
We now know
what we need to
build and how
it’s going to look.
So let’s dive into
the HTML!
in the frame
Wireframes are basic
designs that are incredibly
useful for planning the
user feel of a digital
experience, before a single
line of code is written.
Originally, wireframes
tended to be long lists of
specifications and page
elements but today they
are often very visual
representations of the
app or website that is
going to be built.
If you're thinking of
commissioning an
application, or working
with a developer, often
bringing wireframes
(however sketchy!) can be
a useful starting point for
discussion and design.
2There
TOOLS
is a ton of tools out there
3We’ll
GOOGLE
DOCS
start with some rough sketching. We’re going to use
Random Numbers
Generating a random number
1ThePLANNING
planning process is
for making basic prototypes. You can get a very long way
with tools such as fluidui.com and proto.io. But actually
nothing beats a pencil and paper. The key thing is to get the
idea out of your head and into a medium where you can play
around with it. A huge part of the development process is
Googling, reading, thinking, sketching. Let’s get to it.
Using Javascript to make our app come alive
11
Our snap game app for
smartphone or tablet
will use our own
images. Although it is
a touchscreen game, it
is a web app, running
on a web browser
such as Chrome or
Safari.
3
coding our
content
Carrier
12:00
PLAY SNAP THAT!
Every web page and many of
the apps you know and love
use HTML. It allows us to tell
the browser what everything
is: our logos, paragraphs, any
images, videos and so on.
HTML is a universal language
— it is understood by every
browser, and all smartphones
can run apps built in HTML.
We want our app to be accessible
to everyone. HTML is the only language that everyone’s
device can understand.
1Create
NEWaPLAYTO
PROJECT
new project in the Playto Editor.
2Replace
APP NAME
“Hello, universe!” with the name of your app.
3PutHEADING
1
the app name text inside an <h1> element.
MOBILE FIRST
Web design used to
be mainly for desktop
computers, but as more
and more people now use
mobile devices to access
the web it is best practice
to design "mobile first".
This means thinking about
a mobile user's experience
first, and then extending
your design to desktop.
<h1>PLAY SNAP THAT!</h1>
4Under
PARAGRAPH
your h1 add text for your two players in paragraph
elements.
<p>PLAYER 1</p>
<p>PLAYER 2</p>
5AddCANVAS
a new canvas element above and below your code. A
canvas allows the browser to draw — or create images — in
an area on the page. In our case, we’ll be using the canvas to
display the snap images.
<canvas>Canvas not supported</canvas>
<h1>PLAY SNAP THAT!</h1>
<p>PLAYER 1</p>
<p>PLAYER 2</p>
<canvas>Canvas not supported</canvas>
Turn to page 4 Â
{HTML}
HTML — THE
LANGUAGE OF
CONTENT
HTML, which stands
for HyperText Markup
Language, was developed
by the inventor of the web,
Sir Tim Berners-Lee
in 1989.
The original idea behind
HTML was to write an open
set of rules so that any
browser could interpret
a piece of content and
know where there were
paragraphs, headings,
lists and so on. BernersLee's idea was to allow the
transfer of information
between different
computers, and so HTML
is purely a language
of content.
The fact that HTML is
a "markup language"
means that rather
than writing rules
and instructions for a
computer, we are simply
"marking up" content
with tags.
AN EVOLVING
STANDARD FIRST
HTML is constantly
evolving and developing
as new features come
out. If you use a browser
like Chrome, updates will
happen in the background,
meaning that you'll always
have the latest version.
Aa
THE IMPORTANCE
OF CASES You may have seen
that whether you type
in upper or lower case
matters sometimes when
you’re coding, but not
all the time. It’s usually
best practice to keep
everything lower case
when you are coding, to
make sure that you can
always references files
and elements.
CREATE AN APP IN A DAY
ERROR! Don't panic
Inevitably it won't always work. If you get an error message, go back through and check
every line and punctuation mark carefully. Then check the detail of your error message
for clues. If that doesn't work, help is on hand at our forum — forum.playto.io. Key in
your question and everything will be OK. We’ve also printed a complete rundown of how
your HTML, CSS and JavaScript files should look on the back cover
4
Valid HTML
When Sir Tim Berners-Lee
created the language of HTML,
he set rules for how a page
should be laid out. We need to
add a few more HTML elements
in our page before the content
can be considered “valid”, or as
adhering to the rules of HTML.
HTML is the language we use
for telling the browser what
things are. If you check out your
app in the browser (by clicking
“View Your App” in the Editor) you will notice that there’s no
title in the tab at the top. We need to give the app its own
name, which means adding in a bit more structure.
All HTML pages are made up of two sections: the head for
information about the page, and the body for content the user
sees. The content we’ve written will therefore go in the body.
We can also indent our code. This is purely to show us, as
coders, what’s where. The browser ignores white space.
<html>
<section>
<canvas>Canvas not supported</canvas>
When HTML was
created there were other
competing markup
languages. One of the
reasons HTML has become
so widely used is that
Berners-Lee decided to
make it completely open.
This means that if you
right click on any page on
the web and select "View
page source" you will be
able to see the raw HTML
that makes up the page.
<body>
!DOCTYPE
<html>
<head>
</head>
<body>
<canvas>Canvas not supported</canvas>
</section>
2 GIVE YOUR APP A TITLE
This “title” is not part of the body content. It gives the page a
name, which displays on the tab in your browser and is what
a search engine will use.
<head>
<title>Snap That!</title>
</head>
Doctype tells the browser
what version of HTML
we’re going to be using.
Since HTML is now an
evolving standard (which
means there will never
be an HTML6), it means
that this tag is slightly
less important. However,
for older browsers in
particular, we need to
make sure it is the first
line of our HTML page.
content="width=device-width,
initial-scale=1.0, user-scalable=no">
</head>
<p>PLAYER 2</p>
</>
2 COMMENTS
Let’s add in a comment at the very top of the page to label
who created this page (using your name, of course).

5
Meta and
Structural HTML
Now we have the important
elements in HTML in our code,
we can add a few more meta
and structural elements to help
give our page a name, ensure it
is mobile-ready and add a little
more structure.
1 CREATE A SECTION ELEMENT
AROUND YOUR CONTENT
The “section” element tells
the browser that this area
is a piece of generic content.
keeping up
STANDARDS
HTML is often described
as quite a "forgiving"
language to code in. If you
miss some tags out, like
the head or the body for
example, your website
will probably still display.
However, there are web
standards that every
developer should try to
stick to. By keeping to
these standards you can
be sure that your web
page will look the same on
every device and browser.
CSS (cascading style sheets) is
the way you give your HTML
project a design. It works by
targeting HTML elements and
giving them a list of style
instructions. Look out, though,
because they are spelt the
American way — color, center
and so on.
6
Intro to CSS
<canvas>Canvas not supported</canvas>
scale=1.0, user-scalable=no">
<link href="style.css"
rel="stylesheet">
</head>
3 CREATE A BODY SELECTOR IN CSS
To create an instruction in CSS we first tell it what element to
target, and then we list the changes between curly brackets.
Start your style.css file with:
body { }
4 ALIGN YOUR TEXT AND CHANGE THE FONT FAMILY
Each instruction starts with a property to change, for example
“text-align”. This is followed by a colon and then the value it
should be changed to, for example “center”. Finally we add a
semicolon to tell the browser that we’ve finished.
CSS, THE LANGUAGE
OF DESIGN
CSS stands for cascading
style sheets. It was
developed by Hakon Wium
Lie and Bert Bos in the
early 1990s.
Fundamentally, CSS
gives developers the
ability to breathe life into
HTML – colours, borders,
backgrounds and more.
We’ll be showing you a
variety of CSS commands,
but to see an entire list
of them have a look at
the W3.
font-family:Helvetica;
If you think about it, any
particular part of a design could
be described by how it looks.
You say things like: I want my h1 to be big, bold, red and
centred.
Lots of HTML tags are not
very descriptive. Div, for
example, just stands for
‘division’ and could be
anywhere on a page. With
HTML5 came a number
of new more ‘semantic’
(descriptive) tags – things
like section, footer and
header. These semantic
tags make it easier for
a computer to read and
understand an HTML
page, which is especially
useful for things like
accessibility (so that text
can be enlarged for people
with visual impairments,
for example).
h1 {
font-weight: bold;
text-align: center;
1 CREATE A NEW STYLESHEET
Click the plus sign in the file panel to the left of the Playto
Editor. We can call this new stylesheet anything; style.css is a
sensible name, as it’s short and clear.
2 CONNECT YOUR STYLESHEET TO YOUR HTML
We connect a stylesheet with a link tag. This is like the meta
element — it doesn’t require a closing tag. So, back in the
HTML file:
There are many “word colours”
that have already been defined by
developers. If you want to truly customise your design, you’ll
need to create your own (see “In the pink” panel, far right).
1 BACKGROUND COLOUR
body {
text-align:center;
3 MARGIN AND PADDING
Our h1 will start the game, so we want it to look like a button.
We can give it a bright background colour and then add
padding and margin instructions to give our heading text a
little space to breathe. Padding is a property that adds space
inside an element. Margin adds space around it. These border
instructions give our h1 a solid black border 2 pixels wide.
h1 {
background:yellow;
padding:2%;
margin:2%;
SEPARATION
OF CONCERNS
In computing we often
talk about the idea of the
"separation of concerns",
and in web development
this means having
separate languages and
files for content, design
and interactivity.
This separation is
important because it
makes our code easier
to change. For example,
multiple content files can
reference the same design
file. This means that a
change only needs to be
made in that one style
page and it will affect all
the content pages.
ONLINE
RESOURCES
There are a whole host of
online resources related to
CSS styles. Pretty much
anything you can imagine
from a design perspective
is possible with CSS. One
of the best starting points
is to Google what you
want to do (e.g. ‘make the
background red’) and
find the code.
RGB
}
p {
width:40%;
float:left;
padding:2%;
margin:2%;
border:2px solid black;
border-radius:40px;
background:yellow;
}
5 DISPLAY NONE
Finally, we don’t want our player score to show until play
begins. We can insert “display:none;” to hide the paragraphs
until we are ready to show them.
p {
width:40%;
float:left;
background:LightGrey;
padding:2%;
border:2px solid black;
Our next instruction targets the HTML, body and section
element at the same time. We need to set their heights to 100%
so the canvas height of 42% will be rendered properly.
canvas {
width:100%;
height:42%;
background:yellow;
border-radius:15px;
border-radius:40px;
When Berners-Lee
created the language of
HTML, he decided to use
international (American)
English as it is the most
widely used version. This
can sometimes trip up
those of us in the UK when
we are spelling words like
colour (color) and centre
(center). If you find this
frustrating, just remember
how lucky we are it is
written in our language.
in the pink
There is a set number of
"word colours" that have
already been defined by
developers, but if you truly
want to customise your
design, you'll need to
pick your own.
To do this, you can go
to colorpicker.com, and
you'll see that each colour
has an R, G and B value
(standing for red, green,
blue). Just select a colour
you like, and then copy the
RGB colours to your CSS.
For example, you might
change your heading to a
lovely shade of pink:
h1 {
color: rgb(222, 38, 210);
}
If you'd like to have a bit
of transparency in your
colour, you can also give it
an "alpha" value between
0 and 1, with 0 being
completely transparent
and 1 being opaque.
h1 {
color: rgba(222, 38, 210,
0.8);
}
margin:2%;
divided by the
same language
Once you understand
the principle of CSS, you
can add as many rules
for each bit of the page
as you like. What's great
too is that they're all
interchangeable, so if
you know how to change
the size of a heading, you
can change the size of a
paragraph (or anything
else you like).
border-radius:40px;
font-family:Helvetica;
Our canvas elements will display the snap images. Right now
they are not showing on the page as they don’t have a size.
First we create a new set of instructions for the canvas
elements; then we create changes for the width, height, and
background colour. The last instruction rounds the corners,
adding a curve with a radius of 15 pixels.
BE AS CREATIVE
AS YOU LIKE
border:2px solid black;
2 SIZE AND COLOUR
color: red;
But hold on — that code needs to go in a CSS file, so let’s set
one up.
Designing our
User Interface
Let’s start by giving our apps a
little more colour and structure.
Add a new design instruction to
our body in our stylesheet for
“background”. Note the
international spelling of “color”.
}
}
font-size: 48px;
}
7
height:100%;
Our player paragraphs will eventually display our player
scores. We can style them the same as our h1. However, we
want them to sit next to each other. To do this we need to add
a “float” value so that they sit side by side.
text-align:center;
SEMANTIC
ELEMENTS
html, body, section {
4 FLOAT
body {
Now we’ve got everything set
up, we can start to design our
user interface.
STNMAST2008
}
CSS
}
<meta name="viewport"
<p>PLAYER 1</p>
</html>
INITIAL SCALE
When the iPhone was
launched in 2007,
one of the reasons it
revolutionised the mobile
computing landscape was
because it pretended to
every web page that it had
a much greater width than
the screen size.
This meant an iPhone
could display a site as it
had been designed, and
the user could double-tap
to zoom in and see more.
As we’re designing
specifically for mobiles, we
must get mobile devices to
tell us their true width, and
to automatically have a
zoom level of 1 that makes
up the page.
content="width=device-width, initial-
<title>Snap That!</title>
<h1>PLAY SNAP THAT!</h1>
</body>
3
<meta name="viewport"
<head>

<!DOCTYPE html>
<canvas>Canvas not supported</canvas>
This line probably looks a bit intimidating, but essentially it’s
a “meta” description — a piece of information about our file
that gives the browser information about how to display it.
The initial-scale and user-scalable parts ensure our games
will look correct on a mobile device. This element is selfclosing — it doesn’t need a closing tag.
</head>
Why do we need to add !DOCTYPE? See panel, right.
<p>PLAYER 2</p>
3 TELL THE BROWSER THIS APP IS MOBILE-READY
head -->
1 HTML, BODY AND HEAD
<p>PLAYER 1</p>
A RADICALLY
OPEN LANGUAGE

body {
font-family:Helvetica;
<!DOCTYPE html>
<title>Snap That!</title>
<meta name="viewport"
content="width=device-width,
background:LightGrey;
}
<link href="style.css"
<h1>PLAY SNAP THAT!</h1>
<p>PLAYER 1</p>
<p>PLAYER 2</p>
<canvas>Canvas not
supported</canvas>
</section>
width:100%;
image3.jpg", "http://image-url/
height:42%;
image4.jpg", "http://image-url/
background-color:yellow;
image5.jpg"];
background-image:url("http://
image-url/image1.jpg");
<section>
supported</canvas>
image2.jpg", "http://image-url/
border-radius:15px;
rel="stylesheet">
<canvas>Canvas not
// Define images to use
var imgArray = ["http://image-url/
canvas {
scalable=no">
<body>
// alert("Hello World!");
image1.jpg", "http://image-url/
initial-scale=1.0, user-
</head>
// Test if script.js is working
text-align:center;
<html>
<head>
Script.js
STYLE.CSS
// Create variables for which card
to pick randomly
background-size:cover;
var num1;
background-position:center;
var num2;
}
// Randomly change number
html, body, section {
height:100%;
}
num1 = Math.floor( Math.random() *
imgArray.length );
num2 = Math.floor( Math.random() *
imgArray.length );
h1 {
<script src="script.js"></
script>
</body>
</html>
background:yellow;
// Test random numbers
padding:2%;
console.log("First random number is
margin:2%;
" +num1);
border:2px solid black;
console.log("Second random number is
border-radius:40px;
"+num2);
}
// Create image variables
to get
started go to
THEsundaytimes.
co.uk/learntocode
p {
width:40%;
var img1 = imgArray[ num1 ];
var img2 = imgArray[ num2 ];
float:left;
padding:2%;
// Create css value for background
margin:2%;
image
border:2px solid black;
var url1 = "url("+ img1 +")";
border-radius:40px;
var url2 = "url("+ img2 +")";
background:yellow;
display:none;
}