if ($_SERVER['REQUEST_METHOD'] === 'POST') {
    $name = trim($_POST['name']);
    $email = trim($_POST['email']);

    if (empty($name)) {
        echo "姓名不能为空";
    } elseif (empty($email)) {
        echo "邮箱不能为空";
    } else {
        // 继续后续验证或处理
    }
}

if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
    echo "邮箱格式不正确";
}

$phone = $_POST['phone'];
if (!preg_match('/^1[3-9]\d{9}$/', $phone)) {
    echo "手机号码格式不正确";
}

// 用户名长度 2-20 个字符
if (strlen($name) < 2 || strlen($name) > 20) {
    echo "用户名长度应在2到20之间";
}

// 年龄应在 1-120 之间
$age = (int)$_POST['age'];
if ($age < 1 || $age > 120) {
    echo "请输入有效的年龄";
}

$name = htmlspecialchars($name, ENT_QUOTES, 'UTF-8');

// PDO预处理示例
$stmt = $pdo->prepare("INSERT INTO users (name, email) VALUES (?, ?)");
$stmt->execute([$name, $email]);

$errors = [];

if ($_SERVER['REQUEST_METHOD'] === 'POST') {
    $name  = trim($_POST['name']);
    $email = trim($_POST['email']);
    $phone = trim($_POST['phone']);
    $age   = (int)$_POST['age'];

    if (empty($name)) $errors[] = "姓名不能为空";
    elseif (strlen($name) < 2 || strlen($name) > 20) $errors[] = "用户名长度错误";

    if (empty($email)) {
        $errors[] = "邮箱不能为空";
    } elseif (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
        $errors[] = "邮箱格式不正确";
    }

    if (!preg_match('/^1[3-9]\d{9}$/', $phone)) {
        $errors[] = "手机号格式错误";
    }

    if ($age < 1 || $age > 120) {
        $errors[] = "年龄必须在1-120之间";
    }

    if (empty($errors)) {
        // 数据有效，执行保存操作
        echo "表单提交成功！";
    } else {
        foreach ($errors as $error) {
            echo "<p style='color:red;'>$error</p>";
        }
    }
}