Flow Control

<?php
declare(strict_types=1);

function grade(int $score): string
{
    if ($score >= 90) {
        return "A";
    } elseif ($score >= 75) {
        return "B";
    } elseif ($score >= 50) {
        return "C";
    } else {
        return "F";
    }
}

echo grade(95), " ", grade(80), " ", grade(50), " ", grade(12), "\n";

$cart = [];
if (!$cart) {                       // an empty array is falsy
    echo "Your cart is empty\n";
}

$age = 17;
$hasTicket = true;
if ($age >= 18 && $hasTicket) {
    echo "Enter\n";
} elseif ($age < 18 && $hasTicket) {
    echo "Enter with an adult\n";
}

<?php
$stock = 0;
echo $stock > 0 ? "In stock" : "Sold out", "\n";

$count = 1;
echo "$count item" . ($count === 1 ? "" : "s"), "\n";

// ?? chains: first non-null value wins
$query = ['sort' => null];
$config = ['sort' => 'price'];
$sort = $query['sort'] ?? $config['sort'] ?? 'name';
echo "Sorting by $sort\n";

// a nested decision stays readable as if/elseif, or with brackets
$score = 75;
$band = $score > 90 ? "high" : ($score > 70 ? "mid" : "low");
echo $band, "\n";

<?php
$role = 'editor';

// BUG: no break statements
switch ($role) {
    case 'admin':
        echo "full access\n";
    case 'editor':
        echo "can edit\n";
    case 'viewer':
        echo "can view\n";
}
echo "---\n";

// fixed, and grouping two cases on purpose
switch ($role) {
    case 'admin':
        echo "full access\n";
        break;
    case 'editor':
    case 'author':            // deliberate fall-through: same body
        echo "can edit\n";
        break;
    default:
        echo "can view\n";
}

<?php
function statusText(int $code): string
{
    return match ($code) {
        200, 201, 204 => 'Success',
        301, 302 => 'Redirect',
        404 => 'Not found',
        default => 'Other',
    };
}

echo statusText(201), " | ", statusText(404), " | ", statusText(418), "\n";

// match(true): each arm is a condition, the first true one wins
$bmi = 22.4;
$label = match (true) {
    $bmi < 18.5 => 'underweight',
    $bmi < 25 => 'normal',
    $bmi < 30 => 'overweight',
    default => 'obese',
};
echo $label, "\n";

// strict: the string "1" does not match the int 1
echo match ("1") {
    1 => "int one",
    "1" => "string one",
}, "\n";

<?php
// while: keep going until a condition changes
$balance = 100;
$years = 0;
while ($balance < 200) {
    $balance *= 1.10;         // 10% growth per year
    $years++;
}
echo "Doubled after $years years\n";

// do-while: the body runs once even though the condition is false
$attempts = 0;
do {
    $attempts++;
    echo "Attempt $attempts\n";
} while ($attempts < 0);

// for: a counter; commas allow several expressions
for ($i = 1; $i <= 5; $i++) {
    echo $i * $i, " ";
}
echo "\n";
for ($lo = 0, $hi = 4; $lo < $hi; $lo++, $hi--) {
    echo "[$lo,$hi] ";
}
echo "\n";

<?php
$prices = ['apple' => 30, 'bread' => 45, 'milk' => 28];

foreach ($prices as $item => $price) {
    echo str_pad($item, 6), $price, "\n";
}

$total = 0;
foreach ($prices as $price) {
    $total += $price;
}
echo "Total: $total\n";

// destructure each row in the header
$orders = [[101, 'paid'], [102, 'pending']];
foreach ($orders as [$id, $status]) {
    echo "#$id is $status\n";
}

$users = [['name' => 'Asha', 'age' => 31], ['name' => 'Ravi', 'age' => 27]];
foreach ($users as ['name' => $name, 'age' => $age]) {
    echo "$name ($age)\n";
}

<?php
$nums = [1, 2, 3];
foreach ($nums as &$n) {
    $n = $n * 2;
}
unset($n);              // break the reference straight after the loop

foreach ($nums as $n) {
    // reading only
}
echo implode(",", $nums), "\n";

// often clearer: write through the key, no reference at all
$prices = [10, 20, 30];
foreach ($prices as $i => $price) {
    $prices[$i] = $price * 1.18;
}
echo implode(" ", $prices), "\n";

<?php
for ($i = 0; $i < 6; $i++) {
    if ($i % 2 === 0) {
        continue;            // skip even numbers
    }
    echo $i, " ";
}
echo "\n";

$grid = [[1, 2, 3], [4, -1, 6], [7, 8, 9]];
foreach ($grid as $r => $row) {
    foreach ($row as $c => $value) {
        if ($value < 0) {
            echo "negative at $r,$c\n";
            break 2;         // leaves BOTH loops
        }
    }
}

$words = ['keep', 'skip', 'last'];
foreach ($words as $w) {
    switch ($w) {
        case 'skip':
            continue 2;      // 1 would only leave the switch
    }
    echo "saw $w\n";
}

<?php
$user = 'Asha';
$items = ['Keyboard', 'Mouse'];
?>
<h1>Hello, <?= htmlspecialchars($user) ?></h1>
<?php if ($items): ?>
<ul>
<?php foreach ($items as $item): ?>
  <li><?= htmlspecialchars($item) ?></li>
<?php endforeach; ?>
</ul>
<?php else: ?>
<p>No items.</p>
<?php endif; ?>