Example 2 - Variables and Arrays
Example 1 was not the most compelling example, but it does illustrate how PHP scripts are constructed. Let's extend Example 1 to read some information about the user's environment and display it in a Web page. We will start out with a quick overview of variables in PHP.
Variables
This example introduces some variables to our PHP script. Variables in PHP begin with the $ symbol. PHP uses arrays and variables to store different values. Variables begin with a $ followed by characters, digits, and underscores. Variable names are case sensitive and are assigned with the '= ' operator. Variables are incredibly useful. For example, you may need to keep track of information submitted via a web form or perform calculations on data and store the results.
Here's a simple example:
<?php
$name = 'Elijah';
$yearBorn = 1975;
$currentYear = 2005;
$age = $currentYear - $yearBorn;
print ("$name is $age years old.")
?>
Arrays
An array is an ordered collection of values. Each value can be referenced individually using its position in the array. The first element of an array is in position 0 and the second element is in position 1. Creating arrays in PHP can be done in multiple ways, though the following example is one of the simplest.
$cities = array('Beijing','Oaxaca', 'Habana', 'Jakarta');
For example, to access the second element of the $cities array use $cities[1].
<?php
// create the array
$cities = array('Beijing','Oaxaca', 'Habana', 'Jakarta');
print $cities[2];
?>
Arrays can also be created using a key/value pair combination. These are often referred to as associative arrays or hashes. In a hash each value is associated with a unique key. Unlike list arrays that use a number as an index value, associative arrays use any value. The easiest way to comprehend how a hash works is to think of it as a table. In the following table the country name serves to role as key and the city is the value.
Country (key) |
City (value) |
| Cambodia |
Phnom Penh |
| Lebanon |
Beirut |
| Cuba |
Habana |
| Indonesia |
Jakarta |
| Finland |
Helsinki |
<?php // create the array
$capitals = array(
'Cambodia' => 'Phnom Penh',
'Lebanon' => 'Beirut',
'Cuba' => 'Habana',
'Indonesia' => 'Jakarta',
'Finland' => 'Helsinki'); print ($capitals['Cambodia']); // displays the string "Phnom Penh"
?>
Predefined Variables
Additionally, PHP scripts have access to information about your environment. These variables are stored in special hashes called $_ENV and $_SERVER. Most scripts, which use these variables, only use one or two at a time. The following script accesses 2 different _SERVER variables.
<HTML>
<HEAD><TITLE> Example 2 </TITLE> </HEAD>
<BODY>
<?
// $_SERVER[HTTP_USER_AGENT] and $_SERVER[REMOTE_ADDR] are two of many environment
// variables in PHP. Environment variables store information about
// the user's and server's environment
print("Hello World<br>");
print("You are using $_SERVER[HTTP_USER_AGENT]<br>");
print("Your Internet address is $_SERVER[REMOTE_ADDR]<br>");
?>
</BODY>
</HTML>
Example 2 uses two specific environment variables, $_SERVER[HTTP_USER_AGENT], and $_SERVER[REMOTE_ADDR]. These two variables contain the name of the browser being used and the IP address of the user. The print function displays the values of these variables in the Web page.
Test Example 2
View Source Code
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