解决PHP表单提交与数据库插入失败：提交按钮name属性的关键作用

<button type="submit" class="submit-btn" value="Register"> Register </button>

if (isset($_POST['submit']) ){
    // ... 注册逻辑 ...
}

<!-- ... 省略其他HTML代码 ... -->
<div class="card-back">
    <h2>Memories - A NoteBook</h2>
    <?php 
        if(isset($massage)){
            foreach($massage as $msg){
                echo '<div class="massage" style="color:red;">'.$msg.'</div>'; // 修正了变量名 $massage 为 $msg
            }
        }
    ?>
    <form action="" method="POST" enctype="multipart/form-data"  >
        <input type="text" class=" input-box" placeholder=" Enter Your Name" name="name" required>
        <input type="email" class=" input-box" placeholder=" Enter Your Email " name="email" required>
        <input type="password" class=" input-box" placeholder="Password" name="password" required>
        <input type="password" class=" input-box" placeholder="Re-Type Password" name="cpassword" required>
        <input type="file" class="upload-button" accept="image/jpg, image/jpeg, image/png" name="image" required>
        <!-- 修正后的注册提交按钮 -->
        <button type="submit" name="register" class="submit-btn" value="Register"> Register </button> 
    </form>
    <button type="button" class="btn" onclick="openLogin()"> I've an Account !! </button>
    <a href="">Forgot Password?</a>
</div>
<!-- ... 省略其他HTML代码 ... -->

<?php 

//include config file
include "config.php";

//register user
// 修正后的提交判断条件
if (isset($_POST['register']) ){ 
    $name = mysqli_real_escape_string($conn, $_POST['name']);
    $email = mysqli_real_escape_string($conn, $_POST['email']);
    $password = mysqli_real_escape_string($conn, md5 ($_POST['password']) ); // 注意：md5 不安全，应使用 password_hash
    $cpassword = mysqli_real_escape_string($conn, md5 ($_POST['cpassword']) ); // 注意：md5 不安全

    // 检查文件上传是否成功
    if(isset($_FILES['image']) && $_FILES['image']['error'] === UPLOAD_ERR_OK) {
        $image = $_FILES['image']['name'];
        $image_size = $_FILES['image']['size'];
        $image_tmp_name = $_FILES['image']['tmp_name'];
        $image_folder = "images/".$image;
    } else {
        $massage[] = "图片上传失败或未选择图片";
        // 可以选择在这里终止脚本或提供默认图片
        // exit; 
    }

    //check if email already exists
    // 注意：这里的查询条件 `AND userpassword = '$password'` 不合理，
    // 应该只通过email判断用户是否存在，密码是用于登录验证的。
    $select = mysqli_query($conn, "SELECT * FROM user WHERE email = '$email'") or die(mysqli_error($conn));

    if(mysqli_num_rows($select) > 0){
        $massage[] = "用户已存在！";
    }else{
        if($password != $cpassword){
            $massage[] = "两次输入的密码不匹配！";
        }elseif(isset($image_size) && $image_size > 5097152){ // 确保 $image_size 已设置
            $massage[] = "图片大小应小于5MB！";
        }else{
            $insert = mysqli_query($conn, "INSERT INTO user (username, email, userpassword, Image) VALUES ('$name', '$email', '$password', '$image')") or die(mysqli_error($conn));
            if($insert){
                move_uploaded_file($image_tmp_name, $image_folder);
                $massage[] = "注册成功！";
                header("location: home.php");
                exit(); // 重定向后应立即终止脚本执行
            }else{
                $massage[] = "注册失败！";
            } 
        }  
    }
}