Originally published on zero2php.dev — part of the Zero to PHP course. View this lesson on the original site.

What constants are

Constants are immutable values. Common styles:

<?php

declare(strict_types=1);

const APP_NAME = 'Demo';

define('LEGACY_MAX', 100);

const vs define

const is compile-time friendly for simple scalars; define() can be used dynamically (rare for beginners).

Naming

Name constants clearly—often UPPER_SNAKE_CASE.

Exercise

Declare a const named STEP with value 11, then echo STEP so the output is 11.

From Zero to PHP — PHP foundations: environment, syntax, and values