PHP Variables
Here are the most important things to know about variables in PHP.
- All variables in PHP are denoted with a leading dollar sign ($).
- The value of a variable is the value of its most recent assignment.
- Variables are assigned with the = operator, with the variable on the left-hand side and the expression to be evaluated on the right.
- Variables can, but do not need, to be declared before assignment.
- Variables in PHP do not have intrinsic types - a variable does not know in advance whether it will be used to store a number or a string of characters.
- Variables used before they are assigned have default values.
- PHP does a good job of automatically converting types from one to another when necessary.
- PHP variables are Perl-like.
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.
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:
Example
<?php
$txt = "DeepakOtwar.blogspot.com";
echo "I love $txt!";
?>
The following example will output the sum of two variables:
Example
<?php
$x = 5;
$y = 4;
echo $x + $y;
?>
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:
<?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:
<?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>";
?>
No comments