PHP 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:

Syntax for single-line comments:

 < ?php
$txt = class="phpstringcolor" style="color:brown">"Hello world!";
$x = class="phpnumbercolor" style="color:red">5;
$y = class="phpnumbercolor" style="color:red">10.5;
class="phptagcolor" style="color:red">?> 

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 ($age and $AGE are two different variables)

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 = class="phpstringcolor" style="color:brown">"W3Schools.com";
class="phpnumbercolor" style="color:red"> class="phpkeywordcolor" style="color:mediumblue">
echo class="phpstringcolor" style="color:brown">"I love $txt!";
class="phptagcolor" style="color:red">?> 

The following example will produce the same output as the example above:

 < ?php
$txt = class="phpstringcolor" style="color:brown">"W3Schools.com";
class="phpnumbercolor" style="color:red"> class="phpkeywordcolor" style="color:mediumblue">
echo class="phpstringcolor" style="color:brown">"I love " . $txt . class="phpstringcolor" 
style="color:brown">"!";
class="phptagcolor" style="color:red">?> 

The following example will output the sum of two variables:

 < ?php
class="phpnumbercolor" style="color:red"> $x = class="phpnumbercolor" style="color:red">5;
$y = class="phpnumbercolor" style="color:red">4;
class="phpkeywordcolor" style="color:mediumblue">echo $x + $y;
class="phptagcolor" style="color:red">?> 

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 strict and non-strict requirements, and data type declarations in the PHP 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:

Variable with global scope:

 < ?php
$x = class="phpnumbercolor" style="color:red">5; class="commentcolor" style="color:green">// global scope

class="phpkeywordcolor" style="color:mediumblue">function myTest() {
  class="commentcolor" style="color:green">// using x inside this function will generate an error
  class="phpkeywordcolor" style="color:mediumblue">echo class="phpstringcolor" style="color:brown">"
  < p>Variable x inside function is: $x< /p>";
}
myTest();

class="phpkeywordcolor" style="color:mediumblue">echo class="phpstringcolor" style="color:brown">"
< p>Variable x outside function is: $x< /p>";
class="phptagcolor" style="color:red">?> 

A variable declared within a function has a LOCAL SCOPE and can only be accessed within that function:

Variable with local scope:

 < ?php
class="phpkeywordcolor" style="color:mediumblue">function myTest() {
  $x = class="phpnumbercolor" style="color:red">5; class="commentcolor" style="color:green">// local scope
  class="phpkeywordcolor" style="color:mediumblue">echo class="phpstringcolor" style="color:brown">"
  < p>Variable x inside function is: $x< /p>";
}
myTest();

class="commentcolor" style="color:green">// using x outside the function will generate an error
class="phpkeywordcolor" style="color:mediumblue">echo class="phpstringcolor" style="color:brown">"
< p>Variable x outside function is: $x< /p>";
class="phptagcolor" style="color:red">?> 

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):

 < ?php
$x = class="phpnumbercolor" style="color:red">5;
$y = class="phpnumbercolor" style="color:red">10;

class="phpkeywordcolor" style="color:mediumblue">function myTest()class="phpnumbercolor" 

style="color:red"> {
class="phpnumbercolor" style="color:red">   class="phpkeywordcolor" style="color:mediumblue">
global $x, $y; class="phpnumbercolor" style="color:red">   $y = $x + $y;
class="phpnumbercolor" style="color:red"> }

myTest();
class="phpkeywordcolor" style="color:mediumblue">echo $y; class="commentcolor" style="color:green">
// outputs 15
class="phptagcolor" style="color:red">?> 

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:

 < ?php
$x = class="phpnumbercolor" style="color:red">5;
$y = class="phpnumbercolor" style="color:red">10;
class="phpnumbercolor" style="color:red">
class="phpkeywordcolor" style="color:mediumblue">function myTest()class="phpnumbercolor" 

style="color:red"> {
class="phpnumbercolor" style="color:red">   class="phpglobalcolor" style="color:goldenrod"> $GLOBALS
[class="phpstringcolor" style="color:brown">'y'] = class="phpglobalcolor" style="color:goldenrod">
$GLOBALS[class="phpstringcolor" style="color:brown">'x'] + class="phpglobalcolor" style="color:goldenrod">
$GLOBALS]
[class="phpstringcolor" style="color:brown">'y'];
class="phpnumbercolor" style="color:red"> }
class="phpnumbercolor" style="color:red">
myTest();
class="phpkeywordcolor" style="color:mediumblue">echo $y; class="commentcolor" style="color:green">
// outputs 15
class="phptagcolor" style="color:red">?> 

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
class="phpkeywordcolor" style="color:mediumblue">function myTest()class="phpnumbercolor" 
style="color:red"> {
class="phpnumbercolor" style="color:red">   class="phpkeywordcolor" style="color:mediumblue">
static $x = class="phpnumbercolor" style="color:red">0;
class="phpnumbercolor" style="color:red">   class="phpkeywordcolor" style="color:mediumblue">echo $x;
class="phpnumbercolor" style="color:red">   $x++;
class="phpnumbercolor" style="color:red"> }

myTest();
myTest();
myTest();
class="phptagcolor" style="color:red">?> 

Then, each time the function is called, that variable will still have the information it contained from the last time the function was called.

Note: The variable is still local to the function.