In PHP, variables begin with a dollar sign ($), followed by any number of alphanumeric characters and underscores, but the first character cannot be a number. Thus, the following variable names are valid:
$user _ func _ 5, etc. Unlike keywords, variable names in PHP are case-sensitive, i.e. the
$USER variables are different (Listing 4.1).
Listing 4.1. The dependence of variables on the register. File case_sensitive.php
<?php $user = "John"; $User = "Jack"; $USER = "Michael"; echo $user; // John echo $User; // Jack echo $USER; // Michael
As you can see from Listing 4.1, to assign a value to a variable, you must use the assignment operator
=, which allows you to initialize the variable.
When declaring numeric values, the point appears as a separator for the integer value and the fractional part (Listing 4.2).
Listing 4.2. Declaring numbers. File number_set.php
<?php $number = 1; $var = 3.14;
Initialization by a single value of several variables is allowed due to the fact that the operator
= returns the result of the assignment. In Listing 4.3, the variables
$var are assigned the value 1 in one line by using the
= operator in the chain.
Listing 4.3. Initializing variables with one value. multi_set.php file
<?php $num = $number = $var = 1;