guest_post() 在这里如何工作，输出中的显示问题 - 代码末尾附加和提到的图像

我的问题：

<?php //sqltest.php
//Part 01 - The first part of the code will establish connection with DB using mysqli method
require_once 'login.php';
$conn = new mysqli($hn,$un,$pw,$db);
if ($conn->connect_error) die ($conn->connect_error);
// Part - 02 - Here is the method to delete some data using query by taking input and later checking using isset
if (isset($_POST['delete']) && isset ($_POST['isbn'])){
    $isbn = get_post($conn,'isbn');
    $query ="DELETE FROM classics WHERE isbn = '$isbn'";
    $result = $conn->query($query);
    if (!$result) echo "DELETE failed: $query<br>". $conn->error . "<br><br>";
}
//Part 04 - Here is the method to insert some data using query by taking input by get_post method-(see the last code) and checking using isset
if (isset($_POST['author']) &&
    isset($_POST['title']) &&
    isset($_POST['category']) &&
    isset($_POST['year']) &&
    isset($_POST['isbn'])){
        $author = get_post($conn,'author');
        $title = get_post($conn,'title');
        $category = get_post($conn,'category');
        $year = get_post($conn,'year');
        $isbn = get_post($conn,'isbn');
        $query = "INSERT INTO classics VALUES" . "('$author','$title','$category','$year','$isbn')";
        $result = $conn->query($query);
        if (!$result) echo "INSERT failed:  . $query<br> ". $conn->error. "<br><br>"; 
    }
    //Part - 05 - FORM handler 
    echo <<<_END
    <form action="sqltest.php" 
        method="post">
        <pre> 
        Author <input type = "text" name ="author">
        Title <input type = "text" name = "title">
        Category <input type = "text" name = "category">
        Year <input type = "text" name = "year">
        ISBN <input type = "text" name = "isbn">
        <input type = "submit" value = "ADD RECORD">
        </pre>
        </form>
_END;
// Part - 06 -A new query for showing the whole classics table from DB
$query = "SELECT * FROM classics";
$result = $conn->query($query);
if(!$result) die ("Database access failed: ". $conn->error);
    $rows = $result->num_rows;
    for ($j=0; $j<$rows; ++$j){
        $result->data_seek($j);
        $row = $result->fetch_array(MYSQLI_NUM);
        // Part - 07 The following html code will take the iput for deleting any entry using isbn - refers to 1st part of the code 
        echo <<<_END
        <pre>
        Author $row[0]
        Title $row[1]
        Category $row[2]
        Year $row[3]
        ISBN $row[4]
        </pre>
        <form action = "sqltest.php" method = "post">
        <input type ="hidden" name = "delete" value = "yes">
        <input type = "hiddden" name = "isbn" value = "$row[4]">
        <input type="submit" value = "DELETE RECORD">
        </form>
_END;
    }
    $result->close();
    $conn->close();
    //Part 08 - actually the code begins from here
    function get_post($conn,$var)
    {
        return $conn->real_eascape_string($_POST[$var]); 
        //to avoid special charecter
    }

    ?>

/** 代码工作正常。除了两件事：1.在代码的第7部分中，我提到了要隐藏的ISBN号，只显示删除按钮。但在输出中，它同时显示数字和按钮。2. 带有记录字段的框未根据其设置，这看起来不如预期 - 我使用了 pre，但它仍然显示损坏的输出。