passing two values (one from text, one hidden) using html and php - php

Question

I really struggle here and I spent much time on a solution but it seems that I missing something here.
So I have one page that I have 2 values:
$semesterID = $_GET['semesterID'];
$semesterID_old = $semesterID;
I do this as I want to pass 2 values on my next page. I am trying to do that with this:
<form action=ed_semester_v2.php method="post">
<div id="name">
<h2 class="name">Semester ID</h2>
<input class="subjectname" type="text" name="sem_id" id="sem_id" value= "<?php echo $semesterID; ?> " /> <br>
</div>
<input type="hidden" name="semesterID_old" value= "<?php $semesterID_old; ?>"/>
<button type="submit" value="Submit" name="submit">SAVE CHANGES</button>
</form>
The one $semesterID pass fine to the next page but the semesterID_old no. Just to clarify that the semesterid might change by the user and that's ok.
In my next page, I use this code:
if(isset($_POST['submit'])) {
$first_name=$_POST['sem_id'];
$last_name=$_POST['sem_name'];
$semesterID_old= $_POST['semesterID_old'];
if (empty($last_name)) {
echo "Name is empty";
} else {
$query = "UPDATE semesters SET name = '$last_name' where semesterid='$first_name'";
}
if (!mysqli_query($dbconnect, $query)) {
die('An error occurred when submitting your review.');
} else {
// echo "Thanks for your review.";
}
}
echo $first_name;
echo $semesterID_old;
First_name is fine but semesterID_old says that's undefined.
Any help would be much appreciated.

Answer 1

Just change echo semesterID_old; to echo $semesterID_old;