php表单提交报错显示适当的错误消息代码

html表单：

<form action="form.php" method="post">
  <input type="text" name="username" placeholder="Username">
  <input type="passWord" name="password" placeholder="Password">
  <input type="submit" value="Submit">
</form>

php处理脚本：

<?php
// 获取表单数据
$username = filter_input(INPUT_POST, "username");
$password = filter_input(INPUT_POST, "password");
 
// 验证数据
if (empty($username) || empty($password)) {
  // 显示错误消息
  echo "Please fill out all fields.";
} else {
  // 处理数据
   
  // 显示成功消息
  echo "Form submitted successfully.";
}
?>