Learn PHP Second Step
This tutorial will continue to guide you through
getting started with PHP arrays and loops.
Overview
Beginners: In order to fully understand these concepts, it is highly recommend that you first
read Part 1.
Part two of this series will walk through using core PHP principles
that assist in everyday coding. This includes creating and using arrays
and loops to store and retrieve data when you please.
Array
An array stores multiple values in one
single variable.An
array is what you turn to when you find yourself creating similar
variables over and over. Two words are used when referring to the
contents of an array. Those words are
“key” and
“value”. Every array has at least 1 key and value. They will always come in pairs as the key refers to the value.
There are three types of arrays:
Associative,
Numeric,
Multidimensional.
Multidimensional arrays are simply arrays
within arrays. Let’s take a brief look at the first two.
Associative Arrays
An associative array is helpful in that the
key is
declared by the programmer somewhere thus giving context to the value. For example I will create an array containing personal
information
about myself. Below you will see two ways of laying out the array in
PHP. The purpose of the second is only for organization and ease of
reading. As Jeffrey mentioned in part one of this series, PHP is not
white-space sensitive.
|
<?php
$personalInfo = array(
"name" => "Premjith",
"occupation" => "Web Developer",
"location" => "Calicut,Kerala"
);
?>
|
|
<?php
$personalInfo = array(
'name' => 'Premjith',
'occupation' => 'Web Developer',
'age' => 24,
'location' => 'Calicut,Kerala');
?>
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That’s great and all – but how do I get my information to display in
HTML? I’m glad you asked! It’s very similar to displaying a variable but
you add one little extra piece of data: the
key.
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My name is <?php $personalInfo['name'] ?>
and I am a <?php $personalInfo['occupation'] ?>
in <?php $personalInfo['location'] ?>
and am <?php $personalInfo['age'] ?> years old.
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Wait a second? What’s this is shorthand PHP for . In part one you learned that the
echo command is similar to
print in other languages. The shorthand PHP is just one way to write less code while working.
Numeric Arrays
Sometimes you don’t need to have a word associated with a value within an array. In that case you will use a numeric array which is actually created by default in PHP. Above we used the equal sign
followed
by the greater than sign (=>) to set array values to keys. With
numeric arrays you can simply set the values and the key is assumed
incrementally. Let’s take a look:
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<?php
$personalInfo = array(
'name' => 'Premjith',
'occupation' => 'Web Developer',
'age' => 24,
'location' => 'Calicut,Kerala');
$fruit = array('apple','orange','grapes');
?>
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As you can see we have done nothing but put
values in this array. PHP took care of the keys for us. As far as you beginners are concerned keys
ALWAYS
start at the number 0 and increase by 1 with each new array element. As
you go deeper into learning about arrays you will learn that you can
manipulate them at will – but that is not covered here today. “How do I
know what key to use”, you may ask. The easy way in our example is just
to start at zero and find your element. For example the key for “apple”
is 0, the key for “orange” is 1 and the key for “grapes” is 2. Pretty
simple, huh. Well sometimes your arrays will get huge and go up into the
10s and possibly hundreds. No one wants to sit there and count that
mess. Your first instinct may be to simply run “echo $fruit” but it will
only spit out the word “Array”. PHP gives us a few simple ways to
review our array data. Let’s look at two of them.
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<?php
$personalInfo = array(
'name' => 'Premjith',
'occupation' => 'Web Developer',
'age' => 24,
'location' => 'Calicut,Kerala');
$fruit = array('apple','orange','grapes');
print_r($personalInfo);
var_dump($fruit);
?>
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Note that running these in your browser may produce something quite
nasty looking. The first array will especially be unattractive and
perhaps difficult to read. It may benefit you to throw
<pre> </pre> tags around those two commands so that the white
space is pre-formatted correctly. Assuming you have placed these tags
around the command you should have the following printed back to you:
The first function,
print_r(), will simply print the
structure
and contents of your array. The keys will
be on the left in brackets and the values
will be to the right of the corresponding keys. In the second function, var_dump(), you learn and bit more about your data.
Notice the “age” key in the $personalInfo array. The value is not in
quotes like the other values are. I did this so that you could
distinguish
between two types of data in PHP. Anything in quotes is considered a string and in the case of the “age” data it
is an
integer.
I won’t go into details of the other types of data but I point this out
because the var_dump() function gives you some
useful information.
Notice the first bit which comes in the first line
“array(4)”. The first
bit dumped saying “This is an array and it contains 4 sets of data”.
Going down to the next line you
get your
key you see the first key and then it says
“string(11)”. This is
saying “This is a string and it is 11 characters in length” (keep in
mind that a blank space is considered a character). Jump down to the
“age” key and notice it says int(23). This is
saying “This is an integer with a value of 23″.
Now that you know how to use print_r() and var_dump() we will move on to looping through this
data.
Multidimensional Arrays
As mentioned above a multidimensional array is simply an array that
contains at least one additional array as a value. I will run with the
“personalInfo” example and create an array for a staff team.
|
<?php
$company = array(
'info'=>array(
'name'=>'Company name',
'location'=>'Calicut,Kerala',
'website'=> 'http://company.com'),
'staff'=> array(
array(
'name'=>'Premjith',
'position'=> 'Programer'
),
array(
'name'=>'Anandvenugopal',
'position' => 'Innovation Officer'
),
array(
'name'=>'Shivin',
'position' => 'Operations Officer'
)
)
);
?>
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As you can see multidimensional arrays can get intricate. This is an
odd example because typically this type of data would be stored in a
database and pulled in with PHP later. However, for the sake of learning
about arrays we will start with the data within PHP. The first key in this array is called ‘info’ and it’s value is actually an associative array containing company information. The second key of our $company array is ‘staff’ and it’s value is a numeric array. Let’s take a look at the structure before we begin. Running
print_r($company) will produce the following:
1
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Array ( [info] => Array ([name] =>
Company name
[location] =>Calicut,Kerala
[website] => http:
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Now our company information is ready to be accessed. We access the internal arrays the same way we accessed our personal information earlier. Here’s an example of using data from this multidimensional array:
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<?php
$company['info']['name']
?>
Located in <?php $company['info']['location']?>
and online at <a href="<?php $company['info']['website']?> ">
<?php $company['info']['website']?></a>
Our Programer<?php $company['staff'][0]['name']?>
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Now that we have a grasp on arrays lets jump into loops which will minimize the time we spend parsing the array data.
Loops
Loops will come in quite handy as the amount of data you work with
increases. We’ve gone into arrays so that naturally leads us to loops.
In the last code snippet we listed a staff member within the
<em>$company</em> array. What if we want to cycle, or loop,
through each staff member and display the information in a uniform
fashion? Well in comes the foreach loop. Just like
the function sounds it will do a specific action for
each of the elements within an array or object. It typically
looks like this:
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<?php
foreach($array as $key => $value) {
...some code here
}
?>
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Notice the three variables passed to this function. The first is
simply the array we are working with. The second and third variables are
defined by YOU and can say anything you want. These are what refer to
the array’s data inside the curly brackets. We will look at this in a
moment. But first, just like the echo command has a
shorthand or alternate syntax, foreach has
something that will help transverse between PHP and HTML. This way it
keeps the code as clean as possible. It looks like this:
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<?php foreach($array as $key => $value){ ?>
Some html and some php will go here
<?php } ?>
And i hope you all know the for loop and while loop from some other language the syntax is same as C language. please go through it too....
bye for this time...
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