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:
<?php
$txt = "Hello world!";
$x = 5;
$y = 10.5;
?>
$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.
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 (
$ageand$AGEare two different variables) - 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:
<?php
$txt = "cscientists.com";
echo "I love $txt!";
?>
$txt = "cscientists.com";
echo "I love $txt!";
?>
The following example will produce the same output as the example above:
<?php
$txt = "cscientists.com";
echo "I love " . $txt . "!";
?>
$txt = "cscientists.com";
echo "I love " . $txt . "!";
?>
The following example will output the sum of two variables:
<?php
$x = 5;
$y = 4;
echo $x + $y;
?>
$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 associates a data type to the variable, depending on its value. Since the data types are not set in a strict sense, you can do things like adding a string to an integer without causing an error.
In PHP 7, type declarations were added. This gives an option to specify the data type expected when declaring a function, and by enabling the strict requirement, it will throw a "Fatal Error" on a type mismatch.
You will learn more about the
strict, and non-strict requirements, and the data type declarations in the PHP7 Functions chapter.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:
<!DOCTYPE html>
<html>
<body>
<?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>";
?>
</body>
</html>
<html>
<body>
<?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>";
?>
</body>
</html>
A variable declared within a function has a LOCAL SCOPE and can only be accessed within that function:
<!DOCTYPE html>
<html>
<body>
<?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>";
?>
</body>
</html>
<html>
<body>
<?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>";
?>
</body>
</html>
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):
<!DOCTYPE html>
<html>
<body>
<?php
$x = 5;
$y = 10;
function myTest() {
global $x, $y;
$y = $x + $y;
}
myTest(); // run function
echo $y; // output the new value for variable $y
?>
</body>
</html>
<html>
<body>
<?php
$x = 5;
$y = 10;
function myTest() {
global $x, $y;
$y = $x + $y;
}
myTest(); // run function
echo $y; // output the new value for variable $y
?>
</body>
</html>
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:
<!DOCTYPE html>
<html>
<body>
<?php
$x = 5;
$y = 10;
function myTest() {
$GLOBALS['y'] = $GLOBALS['x'] + $GLOBALS['y'];
}
myTest();
echo $y;
?>
</body>
</html>
<html>
<body>
<?php
$x = 5;
$y = 10;
function myTest() {
$GLOBALS['y'] = $GLOBALS['x'] + $GLOBALS['y'];
}
myTest();
echo $y;
?>
</body>
</html>
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:
<?php
function myTest() {
static $x = 0;
echo $x;
$x++;
}
myTest();
myTest();
myTest();
?>
function myTest() {
static $x = 0;
echo $x;
$x++;
}
myTest();
myTest();
myTest();
?>
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