在 PHP 中验证请求

Question

大家好，他们很难理解如何使用 PHP 验证请求以及如何使用 else/if 语句从我的编码中获取我需要的内容。如果用户未能在我的 HTML 文件的任何三个字段中输入信息，我需要代码来显示活动的错误消息。目前我验证请求的代码如下：

enter code <?php
    $firstName = $_POST['firstName'];
    $phone = $_POST['phone'];       
    $numTickets = $_POST['numTickets'];
    $cost = $numTickets * 35.00;

    $ticketFile = fopen ("ticket-count.txt", "r");
    $totalTickets = fgets($ticketFile);
    fclose ($ticketFile);
        
    
    if (empty($firstName) OR  empty($phone) OR empty($numTickets) )
        print("ERROR: Input is missing!!");

    $availableSeats = 100 - (int)$totalTickets;
    if ($availableSeats < $numTickets) 
    {
        
        if ($availableSeats < 0) 
        {
            $availableSeats = 0;
            print ("<h1>Ticket Purchase</h1>");
            print ("<p>We are sorry. There are $availableSeats tickets available.  We 
                apologize for this inconvenience.</p>");
        }
        
        else
        {
            print ("<h1>Ticket Purchase</h1>");
            print ("<p>We are sorry. There are only $availableSeats tickets available.  Please 
                return to the form using the link below to change your order.</p>");
            print("<p><a href='event.html'>Click here to retun to order form</a></p>");

        }
    }
    else
    {
        print ("<h1>Ticket Purchase</h1>");
        print ("<p>Hi $firstName, You purchased $numTickets tickets. Your cost is $$cost. If we need to contact you we will call you at $phone.</p>");  
        
        $totalTickets = (int)$totalTickets + (int)$numTickets;
        
        $ticketFile = fopen ("ticket-count.txt", "w");
        fputs($ticketFile, "$totalTickets\n" );
        fclose ($ticketFile);
    }
    
    



?>here

现在我知道了我的代码所在的总体思路，它确实会产生错误；但是它仍然显示附加信息。例如，如果我没有在“名字”字段中输入任何信息，它会一直显示在顶部“错误：输入丢失！”然后继续显示电话字段和票数字段。

感谢任何帮助。我觉得我已经阅读了我的书一千遍，并且我尝试使用 youtube 等，但无法真正理解。 再次感谢您的任何意见！

根据要求提供 HTML：

enter code<h1>The Rolling Stones!</h1>
<p>In concert on January 15, 2011. Don't miss this great performance!</p>
<h2>To Purchase Tickets</h2>
<form action = "event.php" method = "post">
<table>
<tr><td>What is your First Name:</td><td><input type = "text" size = "20" name = "firstName"></td><tr>
<tr><td>And your Phone Number?</td><td><input type = "text" size = "20" name = "phone"></td><tr>
<tr><td>How many Tickets do you need?</td><td><input type = "text" size = "20" name = "numTickets"></td><tr>
</table>
<p><input type = "submit" value = "Submit Your Order"></p>
</form>

这里

Answer 1

<?php
    $firstName = $_POST['firstName'];
    $phone = $_POST['phone'];       
    $numTickets = $_POST['numTickets'];
    $cost = (int)$numTickets * 35.00;

    if (empty($firstName) OR  empty($phone) OR empty($numTickets) )
        print("ERROR: Input is missing!!");
    elseif ( !is_numeric($phone) OR !is_numeric($numTickets) )
        print("ERROR: Non-numeric input found!");
    
    else
    {

    
    $ticketFile = fopen ("ticket-count.txt", "r");
    $totalTickets = fgets($ticketFile);
    fclose ($ticketFile);
        
    

    $availableSeats = 100 - (int)$totalTickets;
    if ($availableSeats < $numTickets) 
    {
        
        if ($availableSeats < 0) 
        {
            $availableSeats = 0;
            print ("<h1>Ticket Purchase</h1>");
            print ("<p>We are sorry. There are $availableSeats tickets available.  We 
                apologize for this inconvenience.</p>");
        }
        
        else
        {
            print ("<h1>Ticket Purchase</h1>");
            print ("<p>We are sorry. There are only $availableSeats tickets available.  Please 
                return to the form using the link below to change your order.</p>");
            print("<p><a href='event.html'>Click here to retun to order form</a></p>");

        }
    }
    else
    {
        print ("<h1>Ticket Purchase</h1>");
        print ("<p>Hi $firstName, You purchased $numTickets tickets. Your cost is $$cost. If we need to contact you we will call you at $phone.</p>");  
        
        $totalTickets = (int)$totalTickets + (int)$numTickets;
        
        $ticketFile = fopen ("ticket-count.txt", "w");
        fputs($ticketFile, "$totalTickets\n" );
        fclose ($ticketFile);
    }
    
    }



?>