PHP
5 Variables
Variables
are "containers" for storing information.
Creating
(Declaring) PHP Variables
In PHP, a
variable starts with the $ sign, followed by the name of the variable:
Example
<?php
$txt
= "Hello world!";
$x
= 5;
$y
= 10.5;
?>
After the execution
of the statements above, the variable $txt will hold the value Hello world!,
the variable $x will hold the value 5, and the variable $y will hold the value
10.5.
Note: When
you assign a text value to a variable, put quotes around the value.
Note: Unlike
other programming languages, PHP has no command for declaring a variable. It is
created the moment you first assign a value to it.
Think of
variables as containers for storing data.
PHP
Variables
A variable
can have a short name (like x and y) or a more descriptive name (age, carname,
total_volume).
Rules for
PHP variables:
A variable
starts with the $ sign, followed by the name of the variable
A variable
name must start with a letter or the underscore character
A variable
name cannot start with a number
A variable
name can only contain alpha-numeric characters and underscores (A-z, 0-9, and _
)
Variable
names are case-sensitive ($age and $AGE are two different variables)
Remember
that PHP variable names are case-sensitive!
Output
Variables
The PHP echo
statement is often used to output data to the screen.
The
following example will show how to output text and a variable:
Example
<?php
$txt
= "Omega.com";
echo
"I love $txt!";
?>
The
following example will produce the same output as the example above:
Example
<?php
$txt
= "Omega.com";
echo
"I love " . $txt . "!";
?>
The
following example will output the sum of two variables:
Example
<?php
$x
= 5;
$y
= 4;
echo
$x + $y;
?>
Note: You
will learn more about the echo statement and how to output data to the screen
in the next chapter.
PHP is a
Loosely Typed Language
In the
example above, notice that we did not have to tell PHP which data type the
variable is.
PHP
automatically converts the variable to the correct data type, depending on its value.
In other
languages such as C, C++, and Java, the programmer must declare the name and
type of the variable before using it.
PHP
Variables Scope
In PHP,
variables can be declared anywhere in the script.
The scope of
a variable is the part of the script where the variable can be referenced/used.
PHP has
three different variable scopes:
local
global
static
Global and
Local Scope
A variable
declared outside a function has a GLOBAL SCOPE and can only be accessed outside
a function:
Example
<?php
$x
= 5; // global scope
function
myTest() {
// using x inside this function will
generate an error
echo "<p>Variable x inside
function is: $x</p>";
}
myTest();
echo
"<p>Variable x outside function is: $x</p>";
?>
A variable
declared within a function has a LOCAL SCOPE and can only be accessed within
that function:
Example
<?php
function
myTest() {
$x = 5; // local scope
echo "<p>Variable x inside
function is: $x</p>";
}
myTest();
//
using x outside the function will generate an error
echo
"<p>Variable x outside function is: $x</p>";
?>
You can have
local variables with the same name in different functions, because local
variables are only recognized by the function in which they are declared.
PHP The
global Keyword
The global
keyword is used to access a global variable from within a function.
To do this,
use the global keyword before the variables (inside the function):
Example
<?php
$x
= 5;
$y
= 10;
function
myTest() {
global $x, $y;
$y = $x + $y;
}
myTest();
echo
$y; // outputs 15
?>
PHP also
stores all global variables in an array called $GLOBALS[index]. The index holds
the name of the variable. This array is also accessible from within functions
and can be used to update global variables directly.
The example
above can be rewritten like this:
Example
<?php
$x
= 5;
$y
= 10;
function
myTest() {
$GLOBALS['y'] = $GLOBALS['x'] +
$GLOBALS['y'];
}
myTest();
echo
$y; // outputs 15
?>
PHP The
static Keyword
Normally,
when a function is completed/executed, all of its variables are deleted.
However, sometimes we want a local variable NOT to be deleted. We need it for a
further job.
To do this,
use the static keyword when you first declare the variable:
Example
<?php
function
myTest() {
static $x = 0;
echo $x;
$x++;
}
myTest();
myTest();
myTest();
?>
Then, each
time the function is called, that variable will still have the information it
contained from the last time the function was called.
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