首先让我说一下，我已尝试将下面的代码剪得尽可能小:

        <?php
        // required variables (make them explciit no need for foreach loop)

        $getyear       = (isset($_POST['year'])) ? $_POST['year'] : '';
        $getpass       = (isset($_POST['studentpass'])) ? $_POST['studentpass'] : '';
        $getretypepass = (isset($_POST['retypepass'])) ? $_POST['retypepass'] : '';
        $errormsg      = (isset($errormsg)) ? $errormsg : '';

        $validSubmission = isset($_POST['registerbtn']) && $_POST['year'] && $_POST['studentpass'] && $_POST['retypepass'];

        $min_year = 1;
        $max_year = 10;
        $years    = range($min_year, $max_year); // returns array with numeric values of 1900 - 2012
        $yearHTML = '';
        $yearHTML .= '<select name="year" id="yearDrop">' . PHP_EOL;
        $yearHTML .= '<option value="">Please Select</option>' . PHP_EOL;
        foreach ($years as $year) {
            if (!$validSubmission && isset($_POST['year']) && $year == $_POST['year']) {
                $yearHTML .= "<option value='" . $year . "' selected='selected'>$year</option>" . PHP_EOL;
            } else {
                $yearHTML .= "<option value='" . $year . "'>$year</option>" . PHP_EOL;
            }
        }

        $yearHTML .= '</select>';


        if ((isset($_POST['registerbtn']))) {
            if (in_array($_POST['year'], $years) === true) {
                $getyear = (int) $_POST['year'];
            }
            $getpass       = $_POST['studentpass'];
            $getretypepass = $_POST['retypepass'];


            if ($getyear) {
                if ($getpass) {
                    if (strlen($getpass) <= 5) {
                        $errormsg = "The Password must be a minimum of 6 characters or more";
                    } else {
                        if ($getretypepass) {
                            if ($getpass === $getretypepass) {
                                //perform 2 queries, one query contains $aliasnumrows and other contains $numrows

                                if ($aliasnumrows == 0) {
                                    if ($numrows == 0) {
                                        //perform query which contains $numrows


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

                                            $getyear = "";


                                        } else {
                                            $errormsg = "An error has occured, Student has not been Registered";

                                        }

                                    }

                                    else {
                                        $errormsg = "There is already a Student with that Username";
                                    }
                                }

                                else {
                                    $errormsg = "There is already a Student with that Alias";
                                }
                            }

                            else {
                                $errormsg = "Your Passwords did not match";
                            }
                        }

                        else {
                            $errormsg = "You must retype your Password to Register";
                        }
                    }
                } else {
                    $errormsg = "You must enter in a Password to Register";
                }

            }

        else{
    $errormsg = "You must enter in Student's current Academic Year to Register";
    }

    }

$form = "
<form action='" . htmlentities($_SERVER["PHP_SELF"]) . "' method='post'>
  <table>
  <tr>
  <td></td>
  <td id='errormsg'>$errormsg</td>
</tr>
  <tr>
  <td>Year:</td>
  <td>{$yearHTML}</td>
  </tr>
  <tr>
  <td>Password:</td>
  <td><input type='password' name='studentpass' value='' /></td>  
  </tr>
  <tr>
  <td>Retype Password:</td>
  <td><input type='password' name='retypepass' value='' /></td>  
  </tr>
  <tr>
  <tr>
  <td></td>
  <td><input type='submit' value='Register' name='registerbtn' /></td>
  </tr>
  </table>
  </form>";

  echo $form;

好的，这就是我遇到的问题。我有一个多年的下拉菜单和两个用于输入密码和重新输入密码的文本输入。现在，如果用户从下拉菜单中选择年份并提交表单，则会显示错误消息，指出必须输入密码，并且年份下拉菜单仍显示用户从年份下拉菜单中选择的选项。

我遇到的问题是，如果出现以下任一消息，则下拉选项会返回显示“请选择”。我的问题是，当出现以下错误消息时，如何停止下拉菜单返回“请选择”选项？

$errormsg = "There is already a Student with that Username";
$errormsg = "There is already a Student with that Alias";
$errormsg = "Your Passwords did not match";
$errormsg = "You must retype your Password to Register";

我认为需要更改的代码行在这里:

    $validSubmission = isset($_POST['registerbtn']) && $_POST['year'] && $_POST['studentpass'] && $_POST['retypepass'];