PDO টিউটোরিয়াল (MySQL)

<?php
$stmt = $db->prepare("SELECT * FROM table WHERE id=? AND name=?");
$stmt->execute(array($id, $name));
$rows = $stmt->fetchAll(PDO::FETCH_ASSOC);
?>

$query = $db->prepare("INSERT INTO user (username, password, email, activation) VALUES (:username, :password, :email, :activation)");
        $query = execute([':username' => $username, ':password' => $password, ':email' => $email, ':activation' => $rnd]);
        $affected_rows = $query->rowCount();
        echo $affected_rows;

( ! ) Parse error: syntax error, unexpected '[', expecting ')' in C:\wamp\www\user\function.php on line 73

$query = $db->prepare("INSERT INTO user (username, password, email, activation) VALUES (:username, :password, :email, :activation)");
        $query = execute(array(':username' => $username, ':password' => $password, ':email' => $email, ':activation' => $rnd));

Fatal error: Call to undefined function execute() in C:\wamp\www\user\function.php on line 73

$dbhost = 'localhost';
$dbname = 'student';
$dbuser = 'root';
$dbpass = '';
try {
$pdo = new PDO("mysql:host={$dbhost};dbname={$dbname}", $dbuser, $dbpass);
$pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
$conn = $pdo;
}
catch( PDOException $excepiton ) {
echo "Connection error :" . $excepiton->getMessage();
}

$statement = $pdo->prepare("INSERT INTO tbl_student (name,roll,age) VALUES (?,?,?)");
$statement->execute(array($st_name,$st_roll,$st_age));

$statement = $pdo->prepare("SELECT * FROM tbl_student WHERE id=?");
$statement->execute(array($st_id));
$result = $statement->fetchAll(PDO::FETCH_ASSOC);
foreach($result as $row)
{
echo $row['name'].'<br>';
echo $row['roll'].'<br>';
echo $row['age'].'<br>';
}

$statement = $pdo->prepare("UPDATE arefin SET name=?, roll=? WHERE id=?");
$statement->execute(array($new_name,$new_roll,$st_id));

$statement = $pdo->prepare("DELETE FROM tbl_student");
$statement->execute();