php - Notice: 未定義のインデックス $_POST

Question

私はphpを初めて使用し、連絡フォームを作成しましたが、

注意: 未定義のインデックス: C:\xampp\htdocs\portfolio\portfolio\html\contact.php の名前

行の場合$_POST- 名前、電子メール、メッセージ、および人間。

どうすればエラーを取り除くことができますか??

                                    $name = $_POST['name'];
                                    $email = $_POST['email'];
                                    $message = $_POST['message'];
                                    $from = 'From:'; 
                                    $to = '86376@ict-idcollege.nl'; 
                                    $subject = 'Hello';
                                    $human = $_POST['human'];

                                    $body = "From: $name\n E-Mail: $email\n Message:\n $message";
                                        if (isset($_POST['submit'])) {
                                            if ($name != '' && $email != '') {
                                                if ($human == '4') {                 
                                                    if (mail ($to, $subject, $body, $from)) { 
                                                    echo '<p>Your message has been sent!</p>';
                                                } else { 
                                                    echo '<p>Something went wrong, go back and try again!</p>'; 
                                                } 
                                            } else if ($_POST['submit'] && $human != '4') {
                                                echo '<p>You answered the anti-spam question incorrectly!</p>';
                                            }
                                            } else {
                                                echo '<p>You need to fill in all required fields!!</p>';
                                            }
                                        }
                                ?>
                                <form method="post" action="contact.php">

                                    <label>Name</label>
                                    <input name="name" placeholder="Type Here">

                                    <label>Email</label>
                                    <input name="email" type="email" placeholder="Type Here">

                                    <label>Message</label>
                                    <textarea name="message" placeholder="Type Here"></textarea>

                                    <label>*Wat is 2+2? (Anti-spam)</label>
                                    <input name="human" placeholder="Type Here">

                                    <input id="submit" name="submit" type="submit" value="Submit">

                                </form>