Fundamentals

<?php
$product = "Keyboard";
$price = 49;
$inStock = true;

echo "$product costs $price\n";

$price = $price + 10;   // reassign using the old value
$price += 1;            // the same idea, shorter
echo "New price: $price\n";

$price = "sold out";    // now it holds a string
echo "Price: $price\n";

[$a, $b] = [1, 2];      // assign two variables at once
[$a, $b] = [$b, $a];    // swap them
echo "a=$a b=$b\n";

<?php
$values = [42, 3.5, "42", true, false, null];

foreach ($values as $v) {
    echo "echo: [", $v, "]  type: ", get_debug_type($v), "\n";
}

var_dump(42, "42", false, null);
var_dump(0.1 + 0.2);

print_r(["id" => 7, "tags" => ["php", "web"]]);
echo "\n";

<?php
var_dump("10" + 5);      // numeric string -> int
var_dump("1.5" + 1);     // numeric string -> float
var_dump("10" . 5);      // int -> string
var_dump(7 + true);      // true -> 1
var_dump("3" * "4");     // both converted

function double(int $n): int
{
    return $n * 2;
}
var_dump(double("21")); // coercive mode: "21" is converted to 21

<?php
const TAX_RATE = 0.18;
const APP_NAME = "Shop";
const SIZES = ["S", "M", "L"];     // constants can hold arrays

define("MAX_ITEMS", 10);
if (!defined("DEBUG")) {
    define("DEBUG", false);        // define() can be conditional
}

echo APP_NAME, " allows ", MAX_ITEMS, " items\n";
echo "Tax on 200: ", 200 * TAX_RATE, "\n";
echo "Largest size: ", SIZES[2], "\n";
var_dump(DEBUG);

// built-in and "magic" constants
echo PHP_INT_MAX, "\n";
echo "This is line ", __LINE__, "\n";

<?php
$first = "Ada";
$greeting = "Hello, " . $first;   // . joins strings
$greeting .= "!";                  // .= appends
echo $greeting, "\n";

echo 2 ** 10, "\n";                // power
echo 7 / 2, "\n";                  // / gives a float when needed

$n = 5;
$n *= 3;                           // compound assignment
$n++;                              // increment
echo "n = $n\n";

// the spaceship: -1, 0 or 1 — used for sorting
echo 3 <=> 7, " ", 7 <=> 7, " ", 9 <=> 7, "\n";

// logical operators short-circuit
$loggedIn = false;
echo ($loggedIn && print("never runs")) ? "yes" : "no", "\n";

<?php
$pairs = [
    ['1', 1],
    ['1', '01'],
    ['10', '1e1'],
    [0, 'abc'],
    [null, false],
    [[], false],
    [0, ''],
];

foreach ($pairs as [$a, $b]) {
    $loose = var_export($a == $b, true);
    $strict = var_export($a === $b, true);
    echo str_pad(json_encode($a) . ' vs ' . json_encode($b), 16),
         str_pad("==  $loose", 13), "===  $strict\n";
}

<?php
$settings = ['perPage' => 0, 'title' => ''];

echo $settings['perPage'] ?? 20, "\n";   // 0: the key exists and is not null
echo $settings['perPage'] ?: 20, "\n";   // 20: 0 is falsy
echo $settings['theme'] ?? 'light', "\n"; // missing key, no warning
echo $settings['title'] ?: 'Untitled', "\n";

$age = 20;
echo $age >= 18 ? "adult" : "minor", "\n"; // the full ternary

<?php
var_dump(6 / 2);          // exact: int
var_dump(7 / 2);          // not exact: float
var_dump(intdiv(7, 2));   // whole part only
var_dump(intdiv(-7, 2));  // truncates toward zero, not down
var_dump(7 % 3, -7 % 3);  // remainder takes the sign of the left side
var_dump(fmod(7.5, 2));   // remainder for floats

// the classic use of intdiv and %: split minutes into h:mm
$minutes = 135;
printf("%d:%02d\n", intdiv($minutes, 60), $minutes % 60);

// % 2 tells even from odd
foreach ([4, 7] as $n) {
    echo $n, $n % 2 === 0 ? " is even\n" : " is odd\n";
}

<?php
var_dump((int) "42");       // 42
var_dump((int) "12abc");    // 12: reads the leading digits
var_dump((int) "abc");      // 0: nothing numeric
var_dump((int) 3.99);       // 3: truncates, does not round
var_dump((int) round(3.99)); // 4: round first if you mean it
var_dump((float) "1.5e3");  // 1500
var_dump((string) 7.0);     // "7"
var_dump(intval("ff", 16)); // 255: intval can take a base
var_dump(is_numeric("12abc"), is_numeric(" 12"), is_numeric("1e3"));

<?php
$falsy = [
    'false' => false, '0' => 0, '0.0' => 0.0, '-0.0' => -0.0,
    '""' => "", '"0"' => "0", '[]' => [], 'null' => null,
];
$truthy = [
    '"false"' => "false", '"0.0"' => "0.0", '" "' => " ",
    '-1' => -1, '[0]' => [0], '"00"' => "00",
];

foreach ($falsy + $truthy as $label => $value) {
    echo str_pad($label, 10), var_export((bool) $value, true), "\n";
}

<?php
$user = ['name' => 'Asha', 'nickname' => null, 'visits' => 0];

var_dump(isset($user['name']));      // true
var_dump(isset($user['nickname']));  // false: exists but is null
var_dump(array_key_exists('nickname', $user)); // true: the key is there
var_dump(empty($user['visits']));    // true: 0 is "empty"

// ??= assigns only if the left side is null or undefined
$user['nickname'] ??= $user['name'];
$user['visits'] ??= 100;             // 0 is not null: unchanged
echo "{$user['nickname']} has {$user['visits']} visits\n";

$city = null;
echo "City: " . ($city ?? "unknown") . "\n";

unset($user['visits']);
var_dump(isset($user['visits']));