PHP

<?php
$conn = mysqli_connect("localhost", "root", "", "phpbook");
$user = $_POST['user'];
$pass = $_POST['pass'];
$sql = "SELECT * FROM users WHERE username = '$user' AND password = '$pass'";
echo "SQL sent to the server: " . htmlspecialchars($sql) . "<br>";
$result = mysqli_query($conn, $sql);
if (mysqli_num_rows($result) > 0) {
    $row = mysqli_fetch_assoc($result);
    echo "<b>Welcome {$row['username']} (role: {$row['role']})</b>";
} else {
    echo "Invalid login";
}
?>

<?php
$conn = mysqli_connect("localhost", "root", "", "phpbook");
$stmt = mysqli_prepare($conn,
    "SELECT username, role FROM users WHERE username = ? AND password = ?");
mysqli_stmt_bind_param($stmt, "ss", $_POST['user'], $_POST['pass']);
mysqli_stmt_execute($stmt);
$result = mysqli_stmt_get_result($stmt);
if ($row = mysqli_fetch_assoc($result)) {
    echo "Welcome {$row['username']}";
} else {
    echo "Invalid login – the injection attempt failed.";
}
mysqli_stmt_close($stmt);
mysqli_close($conn);
?>

<?php
$conn = mysqli_connect("localhost", "root", "", "phpbook");
$stmt = mysqli_prepare($conn, "INSERT INTO fees (roll, amount, paid_on) VALUES (?, ?, ?)");
mysqli_stmt_bind_param($stmt, "ids", $roll, $amount, $date);   // bound by reference
$payments = [[101, 2250.00, "2026-07-01"], [102, 3000.00, "2026-07-05"], [101, 2250.00, "2026-08-01"]];
foreach ($payments as [$roll, $amount, $date]) {
    mysqli_stmt_execute($stmt);                                 // uses the current values
    echo "Saved payment id " . mysqli_stmt_insert_id($stmt) . " for roll $roll<br>";
}
mysqli_stmt_close($stmt);

// SELECT with bind_result
$stmt = mysqli_prepare($conn, "SELECT paid_on, amount FROM fees WHERE roll = ? ORDER BY paid_on");
$r = 101;
mysqli_stmt_bind_param($stmt, "i", $r);
mysqli_stmt_execute($stmt);
mysqli_stmt_bind_result($stmt, $paidOn, $amt);
echo "<b>Payments of roll $r</b><br>";
while (mysqli_stmt_fetch($stmt)) {
    echo "$paidOn : Rs. $amt<br>";
}
mysqli_stmt_close($stmt);
mysqli_close($conn);
?>

<?php
$conn = new mysqli("localhost", "root", "", "phpbook");
$stmt = $conn->prepare("SELECT roll, name FROM students WHERE city = ? AND course_id = ?");
$stmt->bind_param("si", $_GET['city'], $_GET['course']);
$stmt->execute();
$result = $stmt->get_result();
echo "Found {$result->num_rows} student(s):<br>";
while ($row = $result->fetch_assoc()) {
    echo "{$row['roll']} – {$row['name']}<br>";
}
$stmt->close();

// PHP 8.1: pass the values to execute() as an array – no bind_param needed
$stmt = $conn->prepare("UPDATE courses SET fee = ? WHERE course_name = ?");
$stmt->execute([4800, "Core PHP"]);
echo "execute([...]): {$stmt->affected_rows} course updated<br>";

// PHP 8.2: execute_query() does prepare + bind + execute in one call
$row = $conn->execute_query("SELECT course_name, fee FROM courses WHERE course_name = ?", ["Core PHP"])
            ->fetch_assoc();
echo "execute_query: {$row['course_name']} now costs Rs. {$row['fee']}";
$conn->close();
?>

<?php
$conn = new mysqli("localhost", "root", "", "phpbook");
$amount = (float) ($_GET['amount'] ?? 0);

function balances(mysqli $conn): string
{
    $out = [];
    foreach ($conn->query("SELECT account, balance FROM ledger") as $r) {
        $out[] = "{$r['account']} = {$r['balance']}";
    }
    return implode(", ", $out);
}
echo "Before: " . balances($conn) . "<br>";
$conn->begin_transaction();
try {
    $stmt = $conn->prepare("UPDATE ledger SET balance = balance + ? WHERE account = ?");
    $stmt->execute([$amount, "Institute"]);             // credit
    $stmt->execute([-$amount, "Asha"]);                 // debit – fails if balance < 0
    $conn->commit();
    echo "Transfer of Rs. $amount committed.<br>";
} catch (mysqli_sql_exception $e) {
    $conn->rollback();
    echo "Transfer of Rs. $amount failed and was rolled back: " . $e->getMessage() . "<br>";
}
echo "After: " . balances($conn);
?>

<?php
$conn = mysqli_connect("localhost", "root", "", "phpbook");
mysqli_begin_transaction($conn);
try {
    $s1 = mysqli_prepare($conn, "INSERT INTO students (roll, name, city, course_id) VALUES (?, ?, ?, ?)");
    mysqli_stmt_execute($s1, [107, "Rohit Jain", "Bhopal", 2]);
    $s2 = mysqli_prepare($conn, "INSERT INTO fees (roll, amount, paid_on) VALUES (?, ?, CURDATE())");
    mysqli_stmt_execute($s2, [107, 3000]);
    mysqli_commit($conn);
    echo "Admission and first payment saved together.<br>";
} catch (mysqli_sql_exception $e) {
    mysqli_rollback($conn);
    echo "Nothing saved: " . $e->getMessage() . "<br>";
}
// try again with the same roll number – the duplicate makes the first INSERT fail
mysqli_begin_transaction($conn);
try {
    mysqli_stmt_execute(mysqli_prepare($conn, "INSERT INTO fees (roll, amount, paid_on) VALUES (?, ?, CURDATE())"), [107, 500]);
    mysqli_stmt_execute(mysqli_prepare($conn, "INSERT INTO students (roll, name) VALUES (?, ?)"), [107, "Duplicate"]);
    mysqli_commit($conn);
} catch (mysqli_sql_exception $e) {
    mysqli_rollback($conn);
    echo "Second attempt rolled back: " . $e->getMessage() . "<br>";
}
$n = mysqli_fetch_row(mysqli_query($conn, "SELECT COUNT(*) FROM fees WHERE roll = 107"))[0];
echo "Fee records for roll 107: $n";
?>

<?php
$conn = new mysqli("localhost", "root", "", "phpbook");
$msg = "";
if ($_SERVER["REQUEST_METHOD"] == "POST") {
    $user = trim($_POST["user"]);
    $pass = $_POST["pass"];
    if (!preg_match("/^[a-z0-9_]{3,30}$/i", $user) || strlen($pass) < 8) {
        $msg = "User name 3–30 letters/digits, password at least 8 characters.";
    } else {
        try {
            $hash = password_hash($pass, PASSWORD_DEFAULT);
            $conn->execute_query("INSERT INTO users (username, password) VALUES (?, ?)", [$user, $hash]);
            $msg = "Registered successfully. You can now log in.";
        } catch (mysqli_sql_exception $e) {
            $msg = ($e->getCode() == 1062) ? "This user name is already taken." : "Registration failed.";
        }
    }
}
?>
<form method="post" style="font-family:Arial;font-size:13px">
  <?= htmlspecialchars($msg) ?><br>
  User <input name="user" id="u"> Password <input type="password" name="pass" id="p">
  <input type="submit" value="Register" id="r">
</form>

<?php
session_start();
$conn = new mysqli("localhost", "root", "", "phpbook");
$row = $conn->execute_query("SELECT id, username, password, role FROM users WHERE username = ?",
                            [$_POST["user"] ?? ""])->fetch_assoc();
if ($row && password_verify($_POST["pass"] ?? "", $row["password"])) {
    session_regenerate_id(true);
    $_SESSION["user_id"] = $row["id"];
    $_SESSION["role"] = $row["role"];
    echo "Login successful – welcome {$row['username']} ({$row['role']})";
} else {
    echo "Invalid user name or password";
}
?>