01 Server-side foundations: challenges

PHP needs an interpreter handling the request.

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>My first PHP page</title>
</head>
<body>
    <h1>Welcome to my website</h1>
    <p><?php echo "PHP created this sentence."; ?></p>
</body>
</html>

Use http://127.0.0.1:8000/index.php with the development server running. View Page Source to see the generated HTML response.

Use . to join text and escape variable text in HTML.

<?php
$name = 'Maya';
$club = 'Art & Design';
echo '<p>Hello, ' . htmlspecialchars($name, ENT_QUOTES, 'UTF-8');
echo '! Welcome to ' . htmlspecialchars($club, ENT_QUOTES, 'UTF-8') . '.</p>';

var_dump shows both type and value.

<?php
var_dump(12);
var_dump('12');
var_dump(true);
var_dump(null);

The types are int, string, bool and NULL. Direct echo of true yields 1; null yields empty output. Use meaningful labels for users.

Order the narrow zero case before the broader low range.

<?php
$capacity = 12;
$members = 10;
$remaining = $capacity - $members;
if ($remaining === 0) {
    echo 'Full';
} elseif ($remaining <= 2) {
    echo 'Almost full';
} else {
    echo 'Places available';
}

Test remaining values 0, 1, 2 and 3. Separately decide how an invalid negative result should be handled.

Put the list wrapper outside the loop body.

<?php
echo '<ol>';
for ($number = 1; $number <= 5; $number++) {
    echo '<li>Task ' . $number . '</li>';
}
echo '</ol>';

Read the old total, add the current number, store the new total.

<?php
$total = 0;
for ($number = 1; $number <= 5; $number++) {
    $total = $total + $number;
}
echo $total;

Intermediate totals: 1, 3, 6, 10, 15. Final output: 15. Resetting total inside the loop would lose earlier values.

Use return, then echo at the caller.

<?php
function placesLeft(int $capacity, int $members): int
{
    return $capacity - $members;
}
echo '<p>' . placesLeft(12, 10) . '</p>';
echo '<p>' . placesLeft(10, 6) . '</p>';

Outputs 2 and 4. The calculation and presentation are separate.

Append with []; output one li for each value.

<?php
$clubs = ['Robotics', 'Art', 'Chess'];
$clubs[] = 'Coding';
echo '<ul>';
foreach ($clubs as $club) {
    echo '<li>' . htmlspecialchars($club, ENT_QUOTES, 'UTF-8') . '</li>';
}
echo '</ul>';

There should be four items without four manually copied output blocks.

Keys label entries inside the array.

<?php
$club = ['name' => 'Robotics', 'capacity' => 12, 'members' => 10];
echo htmlspecialchars($club['name'], ENT_QUOTES, 'UTF-8');

$club is the variable. The string key name selects a value from that array.

Check the last test and the statement that changes the condition.

Use <= 5 to include 5. Without a counter update, a true while condition can stay true indefinitely. Stop the request/server if needed, then fix the update before repeating the test.

Use HTML text escaping at output.

<?php
$clubs = ['Art & Design', '<Robotics>'];
foreach ($clubs as $club) {
    echo '<p>' . htmlspecialchars($club, ENT_QUOTES, 'UTF-8') . '</p>';
}

The browser displays literal characters. Inspect the response source for the escaped forms.

Combine data preparation, functions, foreach, selection and a running total.

<?php
function escapeHtml(string $text): string
{
    return htmlspecialchars($text, ENT_QUOTES, 'UTF-8');
}

function placesLeft(int $capacity, int $members): int
{
    return max(0, $capacity - $members);
}

$clubs = [
    ['name' => 'Robotics', 'capacity' => 12, 'members' => 10],
    ['name' => 'Game Design', 'capacity' => 16, 'members' => 16],
    ['name' => 'Art & Design', 'capacity' => 10, 'members' => 6],
];
$totalMembers = 0;
?>
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>School clubs</title>
</head>
<body>
    <h1>School clubs</h1>
    <ul>
        <?php foreach ($clubs as $club): ?>
            <?php
            $remaining = placesLeft($club['capacity'], $club['members']);
            $totalMembers += $club['members'];
            ?>
            <li>
                <strong><?= escapeHtml($club['name']) ?></strong>:
                <?php if ($remaining > 0): ?>
                    <?= $remaining ?> places available
                <?php else: ?>
                    Full
                <?php endif; ?>
            </li>
        <?php endforeach; ?>
    </ul>
    <p>Total club memberships: <?= $totalMembers ?></p>
</body>
</html>

Expected: Robotics 2 places; Game Design Full; Art & Design 4 places; total club memberships 32. This total counts memberships, not necessarily unique students.

max(0, ...) clamps negative results for display in this sample; it does not validate the underlying data or enforce capacity. Add validation if you extend the requirements.