Syntax, Variables, Types and strict_types

The basics, done the modern way

PHP code lives between <?php tags; files that contain only PHP should omit the closing ?> to avoid accidental whitespace output. Variables start with $ and are created by assignment. PHP has scalar types (int, float, string, bool), compound types (array, object, callable, iterable) and special ones (null, resource). PHP is dynamically typed, but you should add type declarations to parameters, return values and properties. By default PHP coerces scalar arguments (passing "5" to an int parameter becomes 5); adding declare(strict_types=1); at the top of a file makes calls from that file throw a TypeError instead, which catches bugs early. Compare with === (identical: same type and value) rather than == (loose comparison with type juggling); PHP 8 made 0 == "abc" false, but loose comparison still has surprises. Constants are defined with const NAME = value;. Strings in single quotes are literal, while double quotes interpolate variables ("Hello {$user->name}"). The ?? (null coalescing) and ??= operators supply defaults for missing values.

Types, comparisons and null handling

Strict typing turns silent coercion into an error you can fix.

<?php
declare(strict_types=1);

const GST_RATE = 0.18;

function priceWithGst(float $price): float
{
    return round($price * (1 + GST_RATE), 2);
}

echo priceWithGst(100.0), PHP_EOL;     // 118
// priceWithGst("100");               // TypeError under strict_types

var_dump("1" == "01");    // true  (numeric strings compared as numbers)
var_dump("1" === "01");   // false (different strings)
var_dump(0 == "abc");     // false in PHP 8 (was true in PHP 7)

$config = ['timeout' => 30];
$retries = $config['retries'] ?? 3;     // default when the key is missing
$config['region'] ??= 'ap-south-1';    // assign only if not set

Use === by default

Loose == comparisons convert types in ways that are easy to forget, especially with numeric strings, null and booleans. Use === and !== unless you deliberately want conversion.

Quick check: What does declare(strict_types=1) change?

• It makes all variables constant
• It disables arrays
• Calls from that file to typed functions throw TypeError instead of silently coercing scalar types
• It enables the JIT