PHP variables

PHP Variables

• As with algebra, PHP variables can be used to hold values (x=5) or expressions 

(z=x+y). 

• A variable can have a short name (like x and y) or a more descriptive name (age, 

carname, total_volume). 

• Rules for PHP variables: 

o A variable starts with the $ sign, followed by the name of the variable 

o A variable name must start with a letter or the underscore character 

o A variable name cannot start with a number 

o A variable name can only contain alpha-numeric characters and underscores 

(A-z, 0-9, and _ ) 

o Variable names are case sensitive ($y and $Y are two different variables) 

Creating (Declaring) PHP Variables 

• PHP has no command for declaring a variable. 

• A variable is created the moment you first assign a value to it: 

Example:-

<?php 

$txt="Hello world!"; 

$x=5; 

$y=10.5; 

?> 

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: 

o local 

o global 

o static 

Local and Global Scope 

• A variable declared outside a function has a GLOBAL SCOPE and can only be 

accessed outside a function. 

• A variable declared within a function has a LOCAL SCOPE and can only be 

accessed within that function. 

• The following example tests variables with local and global scope: 

Example 

<?php 

$x=5; // global scope 

function myTest() { 

 $y=10; // local scope 

 echo "<p>Test variables inside the function:</p>"; 

 echo "Variable x is: $x"; 

 echo "<br>"; 

 echo "Variable y is: $y"; 

} 

myTest(); 

echo "<p>Test variables outside the function:</p>";

echo "Variable x is: $x"; 

echo "<br>"; 

echo "Variable y is: $y"; 

?> 

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 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(); 

?>