Php 下拉菜单返回到“显示”；请选择"；和失败/成功消息未出现

下面的代码有两个问题

 <?php

$validSubmission = isset($_POST['resetpass']) && $_POST['students'] && $_POST['newpass'] && $_POST['confirmpass'];


$sql = "SELECT StudentUsername, StudentForename, StudentSurname FROM Student ORDER BY StudentUsername";

$sqlstmt = $mysqli->prepare($sql);

$sqlstmt->execute();

$sqlstmt->bind_result($dbStudentUsername, $dbStudentForename, $dbStudentSurname);

$students = array(); // easier if you don't use generic names for data 

$studentHTML = "";
$studentHTML .= '<select name="students" id="studentsDrop">' . PHP_EOL;
$studentHTML .= '<option value="">Please Select</option>' . PHP_EOL;

$outputstudent = "";

while ($sqlstmt->fetch())
{
    $student   = $dbStudentUsername;
    $firstname = $dbStudentForename;
    $surname   = $dbStudentSurname;

    if (!$validSubmission && isset($_POST['students']) && $student == $_POST['students'])
    {
        $studentHTML .= "<option value='" . $student . "' selected='selected'>" . $student . " - " . $firstname . " " . $surname . "</option>" . PHP_EOL;
    }
    else
    {
        $studentHTML .= "<option value='" . $student . "'>" . $student . " - " . $firstname . " " . $surname . "</option>" . PHP_EOL;
    }

}


$studentHTML .= '</select>';

$errormsg = (isset($errormsg)) ? $errormsg : '';

if (isset($_POST['resetpass']))
{
    //get the form data
    $studentdrop = (isset($_POST['students'])) ? $_POST['students'] : '';
    $newpass     = (isset($_POST['newpass'])) ? $_POST['newpass'] : '';
    $confirmpass = (isset($_POST['confirmpass'])) ? $_POST['confirmpass'] : '';

    //make sure all data was entered
    if ($studentdrop != "")
    {
        if ($newpass)
        {
            if (strlen($newpass) <= 5)
            {
                $errormsg = "Your Password must be a minimum of 6 characters or more";
            }
            else
            {
                if ($confirmpass)
                {
                    if ($newpass === $confirmpass)
                    {
                        //Make sure password is correct
                        $query = "SELECT StudentUsername FROM Student WHERE StudentUsername = ?";
                        // prepare query
                        $stmt  = $mysqli->prepare($query);
                        // You only need to call bind_param once
                        $stmt->bind_param("s", $username);
                        // execute query
                        $stmt->execute();
                        // get result and assign variables (prefix with db)
                        $stmt->bind_result($dbStudentUsername);
                        //get number of rows
                        $stmt->store_result();
                        $numrows = $stmt->num_rows();

                        if ($numrows == 1)
                        {
                            //encrypt new password
                            $newpassword = md5(md5("93w" . $newpass . "ed0"));

                            //update the db

                            $updatesql = "UPDATE Student SET StudentPassword = ? WHERE StudentUsername = ?";
                            $update    = $mysqli->prepare($updatesql);
                            $update->bind_param("ss", $newpassword, $username);
                            $update->execute();

                            //make sure the password is changed

                            $query = "SELECT StudentUsername, StudentPassword FROM Student WHERE StudentUsername = ? AND StudentPassword = ?";
                            // prepare query
                            $stmt  = $mysqli->prepare($query);
                            // You only need to call bind_param once
                            $stmt->bind_param("ss", $username, $newpassword);
                            // execute query
                            $stmt->execute();
                            // get result and assign variables (prefix with db)
                            $stmt->bind_result($dbStudentUsername, $dbStudentPassword);
                            //get number of rows
                            $stmt->store_result();
                            $numrows = $stmt->num_rows();

                            if ($numrows == 1)
                            {
                                $errormsg = "<span style='color: green'>Student " . $student . " - " . $firstname . " " . $surname . " has been Registered</span>";

                            }
                            else
                            {
                                $errormsg = "An error has occured, the Password was not Reset";
                            }
                        }
                    }
                    else
                    {
                        $errormsg = "Your New Password did not Match";
                    }
                }
                else
                {
                    $errormsg = "You must Confirm your New Password";
                }
            }
        }
        else
        {
            $errormsg = "You must Enter your New Password";
        }

    }
    else if ($studentdrop == "")
    {
        $errormsg = "You must Select a Student";
    }

} 

$username（第72行及以后）从未设置。我想这应该是来自'studentdrop'吧

这意味着您将更新其中的StudentUsername=''，这将失败

要帮助您调试，请执行以下操作：

1. Turn on warning and notices in the error handler for writing code ( error_reporting(E_ALL); ) as it will reveal problems like this
2. As opposed to constantly counting the rows, you can save time in that the bind_result/store_value won't work unless you got a result. So you can check that value you get in bind_result - and if you had checked that `$dbStudentUsername == $username` in line 78, then it would have also thrown a wobbly at that stage.
3. When you've done the "update", you can check the number of "affected rows"; if this > 0 then the password has been updated; no need for a secondary DB query.

希望有帮助
我能问你一个问题吗Robbie如果你不介意的话，我把所有的
$username
都改成了
$student
，现在如果我选择一个StudentUsername
u0867587
的学生，当我填写并提交表格时，它在成功消息中显示学生
u0753334
已成功重置其密码？你知道这是为什么吗？这是因为
$student
在while循环中，所以只有while循环中的任何东西才能使用
$student
？如果是这样，那么我应该将其更改为或能够检索
$student
变量吗？$student将是该获取循环中的最后一个变量-因此您将更改最后一个用户的密码，而不是所选用户的密码。据我所知，您只需将（原始）$username引用更改为$studentdrop（这是帖子中的值）即可使其正常工作。