PHP Variables

A variable is a name that holds a value. In PHP every variable starts with $.

Assigning

<?php
$name   = 'Ada';
$age    = 36;
$active = true;
$ratio  = 0.382;
$friends = ['Grace', 'Linus', 'Margaret'];

PHP is dynamically typed

Variables don't have a fixed type — the value does. Reassigning is fine:

$x = 1;          // int
$x = 'hello';    // now a string
$x = [1, 2, 3];  // now an array

Naming rules

• Start with $, then a letter or underscore. After that letters, digits, underscores.
• Case-sensitive — $user and $User are different.
• Convention: camelCase for variables, PascalCase for classes, UPPER_SNAKE for constants.

Reference vs value

$a = 10;
$b = $a;       // copy of value
$b = 99;
echo $a;       // 10 — unaffected

$a = [1, 2, 3];
$c = &$a;      // c is a reference to a
$c[] = 4;
print_r($a);   // [1, 2, 3, 4]

Type hints (PHP 7+)

Functions and properties can declare types so PHP enforces them:

class User {
    public string $name;
    public int $age;
}

Example

<?php
$name = 'Ada';
$age  = 36;
$active = true;
echo "$name is $age and active=$active";

Exercise

Test yourself