Variables and Data Types

Variables begin with $ and are case-sensitive. Values include bool, int, float, string, array, object, resource, callable, iterable, and null. Runtime types can change unless declarations constrain them.

Practical example

<?php
$count = 7;
$ratio = 0.75;
$active = true;
$items = ['forms', 'PDO'];
if (!is_int($count)) { throw new TypeError('integer required'); }

Use get_debug_type for diagnostics and is_* predicates for contracts. Type juggling can surprise comparisons and arithmetic, so validate external data and prefer strict equality. Nullable, missing, empty, and invalid are different domain states.