title: Use PHP Variable according to Select DropDown
body: <p>I am trying to change to which php variable to use according to Select Dropdown selection.
  I am aware of how to change the value using jQuery .change but in this case as I am using a variable and php runs on page load and have nothing to do with jquery so I am using two variables but do not know how to use, please help.</p>
  
  <p>Below are the two php variables:</p>
  
  <pre><code>$str201 = '21|'.$paygate_id.'|'.$name.'|'.$amount.'|'.$currency.'|'.$return_url.'|'.$transaction_date.'|'.$start_date.'|'.$end_date.'|201|NO||'.$key;
  $str202 = '21|'.$paygate_id.'|'.$name.'|'.$amount.'|'.$currency.'|'.$return_url.'|'.$transaction_date.'|'.$start_date.'|'.$end_date.'|202|NO||'.$key;
  </code></pre>
  
  <p>Select DropDown</p>
  
  <pre><code>&lt;select name="selectFrequency" id="selectFrequency"&gt;
    &lt;option value=""&gt;- Select -&lt;/option&gt;
    &lt;option value="201"&gt;1&lt;/option&gt;
    &lt;option value="202"&gt;2&lt;/option&gt;
  &lt;/select&gt;
  </code></pre>
  
  <p>Hidden Input of which I need to change php variable on select change:</p>
  
  <pre><code>&lt;input type="hidden" name="CHECKSUM" value="'.md5($str).'"&gt;
  </code></pre>