if (!isset($_POST['fname'], $_POST['lname'], $_POST['email'], $_POST['mobile_number'], $_POST['password'], $_POST['confirm_password'])) {
  exit ('Please fill in all fields.');
}

<?php
session_start();
require_once "config.php";

// 檢查所有必填字段是否都已填寫且不為空
// 使用 || 邏輯運(yùn)算符，只要有一個(gè)字段為空，就執(zhí)行錯(cuò)誤處理
if (empty($_POST['fname']) || empty($_POST['lname']) || empty($_POST['email']) || empty($_POST['mobile_number']) || empty($_POST['password']) || empty($_POST['confirm_password'])) {
    exit('Please fill in all fields.');
}

// 獲取并初步清理表單數(shù)據(jù)
// 使用 trim() 移除字符串兩端的空白字符
$fname = trim($_POST['fname']);
$lname = trim($_POST['lname']);
$email = trim($_POST['email']);
$mobile_number = trim($_POST['mobile_number']);
$password = $_POST['password']; // 密碼不應(yīng)trim，因?yàn)榭崭窨赡苁怯行ё址?$confirm_password = $_POST['confirm_password'];

// 進(jìn)一步的驗(yàn)證：例如密碼確認(rèn)
if ($password !== $confirm_password) {
    exit('Passwords do not match.');
}

// 數(shù)據(jù)庫(kù)操作
if ($stmt = $db->prepare('INSERT INTO accounts (fname, lname, email, mobile_number, password) VALUES (?, ?, ?, ?, ?)')) {
    // 綁定參數(shù)：s代表字符串。這里有5個(gè)字符串參數(shù)。
    // 注意：參數(shù)類型字符串必須與實(shí)際參數(shù)數(shù)量匹配，且參數(shù)順序必須與SQL語(yǔ)句中的占位符順序一致。
    $param_fname = $fname;
    $param_lname = $lname;
    $param_email = $email;
    $param_mobile_number = $mobile_number;
    $param_password = password_hash($password, PASSWORD_DEFAULT); // 對(duì)密碼進(jìn)行哈希處理

    mysqli_stmt_bind_param($stmt, "sssss", $param_fname, $param_lname, $param_email, $param_mobile_number, $param_password);

    if (mysqli_stmt_execute($stmt)) {
        // 注冊(cè)成功，重定向到登錄頁(yè)面
        header("Location: index.php");
        exit(); // 重定向后立即退出腳本
    } else {
        echo "Oops! Something went wrong! Please try again later.";
    }
    mysqli_stmt_close($stmt);
} else {
    echo "Database prepare error: " . $db->error; // 打印SQL準(zhǔn)備錯(cuò)誤
}

// 確保在所有可能的情況下都關(guān)閉數(shù)據(jù)庫(kù)連接（如果使用面向?qū)ο箫L(fēng)格，通常在腳本結(jié)束時(shí)自動(dòng)關(guān)閉）
// 或者在非持久連接的情況下，在所有操作完成后手動(dòng)關(guān)閉
// mysqli_close($db); // 如果config.php中 $db 是通過(guò) mysqli_connect 創(chuàng)建的
?>

<form class="form form_hidden" id="createAccount" action="createaccount.php" method="post">
  <h1 class="form_title">Create Account</h1>

  <div class="form_text error_message"></div>

  <input class="" type="text" placeholder="First Name" name="fname" id="fname" required />
    <div class="form_text input_error_message"></div>
  <input class="" type="text" placeholder="Last Name" name="lname" id="lname" required />
    <div class="form_text input_error_message"></div>
  <input class="" type="email" placeholder="Email Address" name="email" id="email" required />
    <div class="form_text input_error_message"></div>
  <input class="" type="tel" placeholder="(123) 456-7890" name="mobile_number" id="mobile_number" required />
    <div class="form_text input_error_message"></div>
  <input class="" type="password" placeholder="Password" name="password" id="password" required />
    <div class="form_text input_error_message"></div>
  <input class="" type="password" placeholder="Confirm Password" name="confirm_password" id="confirm_password" required />
    <div class="form_text input_error_message"></div>

  <button type="submit">Continue</button>

  <p class="form_text">
    Already have an account? <a href="./" id="linkLogin">Sign in!</a>
  </p>
</form>