我正在練習 PHP 和數據庫創建，并且想根據輸入錯誤更改我的消息。我不知道如何將更改后的消息傳遞回去，并且希望得到任何幫助。這是我的注冊頁面<main>    <h1>Signup<h1>        <h3>        <?php                           echo $errorMsg;             ?>     <h3>      <form action="includes/signup.inc.php" method="post">    <input type="text" name="uid" placeholder="Username">    <input type="text" name="mail" placeholder="E-mail">    <input type="password" name="pwd" placeholder="Password">    <input type="password" name="pwd_repeat" placeholder="Repeat Password">    <button type="submit" name="signup-submit">Submit</button>    <form></main>這是我的處理頁面if(isset($_POST['signup-submit'])){require 'dbh.inc.php';$Name = $_POST['uid'];$Email= $_POST['mail'];$Password = $_POST['pwd'];$PasswordRepeat = $_POST['pwd_repeat'];if(empty($Name) || empty($Email) || empty($Password) || empty($PasswordRepeat)){    header("Location: ../signup.php?error=emptyfields=1");                          //Check if any field is empty    exit();}else if(!filter_var($Email, FILTER_VALIDATE_EMAIL) && !preg_match("/^[a-zA-Z0-9]*$/", $Name)){        header("Location: ../signup.php?error=invalidamil&uid");                        //Check if username and email is valid input    exit();}else if(!filter_var($Email, FILTER_VALIDATE_EMAIL)){    header("Location: ../signup.php?error=invalidamil&uid=".$Name);                     //Check if email is valid input    exit();}else if($Password !== $PasswordRepeat){    header("Location: ../signup.php?error=passwordCheck&uid=".$Name."&mail=".$Email);   // Check if passwords don't match    exit(); }$sql2 = "SELECT UserName FROM dbo.MainTable WHERE UserName = ?";$params2 = array($Name, SQLSRV_PARAM_IN);$stmt2 = sqlsrv_query($conn, $sql2, $params2);if($stmt2 === false){    die(print_r(sqlsrv_errors(), true));    exit();}我不確定在哪里放置更改消息變量，因為我無法讓它在 if 語句中工作。