PHP Variables

In PHP, a variable is a storage container for a value, such as a number, a string, or an array. Variables in PHP are denoted by a dollar sign ($) followed by the name of the variable. The name of the variable must start with a letter or an underscore, and can only contain letters, numbers, and underscores.

Here are a few examples of how to declare and assign values to variables in PHP:

$name = "John";
$age = 25;
$isStudent = true;
$grades = array(90, 80, 70);

The value of a variable can be changed by assigning a new value to it, like so:

$name = "Jane";
$age = $age + 1;
$isStudent = false;

In PHP, variables do not need to be declared before they are used, and their type is determined by the value that is assigned to them. So, for example, the variable $name above is a string, $age is an integer, $isStudent is a boolean and $grades is an array.

It is also possible to use the keyword var to define a variable, but it is considered legacy and it's not recommended anymore.

In addition to the basic data types such as strings, integers, and booleans, PHP also supports more complex data types such as arrays and objects. PHP also has a set of special constants such as PHP_VERSION or PHP_INT_MAX that gives information about the PHP installation or platform respectively.