Dynamic dropdowns

<!--sample_cess.php-->


<html>
<body>
  <?php session_start();
  $track=$_SESSION['track_sess'];
  $sem=$_SESSION['sem_sess'];
  $strand=$_SESSION['strand_sess'];

  ?>
 <label>Track</label><br>
<select name="track" onchange="window.location='session.php?track='+this.value">
<option></option>
<option value="Academic" <?php echo $track==='Academic' ? 'selected' : '' ?>>Academic</option>
<option value="Technical-Vocational-Livelihood" <?php echo $track==='Technical-Vocational-Livelihood' ? 'selected' : '' ?>>Technical-Vocational-Livelihood</option>
</select><br>

<label>Semesters</label><br>
<select name="semester" onchange="window.location='session.php?sem='+this.value">
  <option></option>
  <option value="First semester" <?php echo $sem==='First semester' ? 'selected' : '' ?>>First semester</option>
  <option value="Second semester" <?php echo $sem==='Second semester' ? 'selected' : '' ?>>Second semester</option>
</select><br>

<label>Strands</label><br>
<select name="strands" onchange="window.location='session.php?strand='+this.value">
  <?php if($track=='Academic' && $sem=='First semester'){ ?>
  <option></option>
  <option value="Accountancy" <?php echo $strand==='Accountancy' ? 'selected' : '' ?>>Accountancy</option>
  <option value="Business and Management (ABM)" <?php echo $strand==='Business and Management (ABM)' ? 'selected' : '' ?>>Business and Management (ABM)</option>
  <option value="Science, Technology Engineering and Mathematics (STEM)" <?php echo $strand==='Science, Technology Engineering and Mathematics (STEM)' ? 'selected' : '' ?>>Science, Technology Engineering and Mathematics (STEM)</option>
  <option value="Humanities and Social Sciences (HUMSS)" <?php echo $strand==='Humanities and Social Sciences (HUMSS)' ? 'selected' : '' ?>>Humanities and Social Sciences (HUMSS)</option>
  <option value="General Academic (GAS)" <?php echo $strand==='General Academic (GAS)' ? 'selected' : '' ?>>General Academic (GAS)</option>
<?php }
if($track=='Technical-Vocational-Livelihood' && $sem=='First semester'){
  ?>
  <option></option>
  <option value="Information and Communications Technology (ICT)" <?php echo $strand==='Information and Communications Technology (ICT)' ? 'selected' : '' ?>>Information and Communications Technology (ICT)</option>
  <option value="Home Economics (HE)" <?php echo $strand==='Home Economics (HE)' ? 'selected' : '' ?>>Home Economics (HE)</option>
<?php }
if($track=='Academic' && $sem=='Second semester'){
?>
<option></option>
<option value="1st subject" <?php echo $strand==='1st subject' ? 'selected' : '' ?>>1st subject</option>
<option value="2st subject" <?php echo $strand==='2st subject' ? 'selected' : '' ?>>2nd subject</option>
<option value="3st subject" <?php echo $strand==='3st subject' ? 'selected' : '' ?>>3rd subject</option>
<?php }
if($track=='Technical-Vocational-Livelihood' && $sem=='Second semester'){
  ?>
  option></option>
  <option value="1st subject" <?php echo $strand==='1st subject' ? 'selected' : '' ?>>1st subject</option>
  <option value="2st subject" <?php echo $strand==='2st subject' ? 'selected' : '' ?>>2nd subject</option>
  <option value="3st subject" <?php echo $strand==='3st subject' ? 'selected' : '' ?>>3rd subject</option>
  <?php } ?>
</select>

<br><br><br>

  <div id="result">
    <?php
   echo $track."<br>". $_SESSION['sem_sess']."<br>". $_SESSION['strand_sess']; ?>
  </div>

</body>
</html>

<!--session.php-->
<?php
session_start();
  $track=$_GET["track"];
  $sem=$_GET["sem"];
  $strand=$_GET["strand"];

if(isset($track)){
 $_SESSION['track_sess']=$track;
}
if(isset($sem)){
  $_SESSION['sem_sess']=$sem;
}
if(isset($strand)){
 $_SESSION['strand_sess']=$strand;
}

header("location:sample_sess.php");
 ?>