UserController.php

class UserController {
    private $input = array(
        2 => [
            'user_id' => 2,
            'user_name' => 'Mr. Abdul Kalam',
            'age' => 53,
        ]
    );
    private $user_id = 2;

    function add() {
        if (isset($this->$input[$this->user_id])) {
            $user_name = $this->input[$this->user_id]['user_name'];
            $age = $this->input[$this->user_id]['age'];
            $connection =  new PDO("mysql:host=localhost;dbname=userdatabase", 'root', '1234');
            $connection->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

            // prepare sql and bind parameters
            $stmt = $connection->prepare("INSERT INTO users(id, username, age)
                VALUES (:id, :username , :age)");
            $stmt->bindParam(':id', $this->user_id);
            $stmt->bindParam(':username', $user_name);
            $stmt->bindParam(':age', $age);
            $stmt->execute();
        }
    }

    function update() {
        if (isset($this->$input[$this->user_id])) {
            $user_name = $this->input[$this->user_id]['user_name'];
            $age = $this->input[$this->user_id]['age'];
            $connection =  new PDO("mysql:host=localhost;dbname=userdatabase", 'root', '1234');
            $connection->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

            // prepare sql and bind parameters
            $stmt = $connection->prepare("UPDATE users SET username=:username, age=:age where id=:id ");
            $stmt->bindParam(':id', $this->user_id);
            $stmt->bindParam(':username', $user_name);
            $stmt->bindParam(':age', $age);
            $stmt->execute();
        }
    }
}