title: PHP: Disable Enable text box on the basis of dropdown
body: <p>I'm new to PHP. i am trying to create some html code within a php function as below.</p>
  
  <hr>
  
  <pre><code>$str .="&lt;/div&gt;
                  &lt;div class='cls_setpadding'&gt;
                      &lt;form method='get' action='homepage.php'&gt;
                      &lt;div class='cls_caller_options'&gt;
                          &lt;select name='test'&gt;
                              &lt;option value='allcaller'&gt;".getResourceStrings('msg_allcaller',$lng)."&lt;/option&gt;
                              &lt;option value='specialcaller'&gt;".getResourceStrings('msg_splcaller',$lng)."&lt;/option&gt;
                          &lt;/select&gt;&lt;br /&gt;
                      &lt;/div&gt;
                      &lt;div class='cls_msg_splcaller'&gt;";
          $str .=      getResourceStrings('msg_spcallaer',$lng);          
          $str .="    &lt;/div&gt;
                      &lt;div style='padding-top:2%'&gt;&lt;/div&gt;
                      &lt;div class='cls_search_box'&gt;
                      &lt;input type='hidden' name='function' value='Buysuccess' /&gt;
                      &lt;input type='hidden' name='vcode' value='".$vcode."' /&gt;";
                      if($testmsisdnheader != ""){
                          $msisdn_header = getheader();
                          $str .="&lt;input type='hidden' name='".$msisdn_header."' value='".$msisdn."' /&gt;";
                      }
  
          $str .="    &lt;input type='text' onkeydown='return ( event.ctrlKey || event.altKey 
                      || (47&lt;event.keyCode &amp;&amp; event.keyCode&lt;58 &amp;&amp; event.shiftKey==false) 
                      || (95&lt;event.keyCode &amp;&amp; event.keyCode&lt;106)
                      || (event.keyCode==8) || (event.keyCode==9) 
                      || (event.keyCode&gt;34 &amp;&amp; event.keyCode&lt;40) 
                      || (event.keyCode==46) )' name='cbsmsisdn' maxlength='12' disabled='true'/&gt;&lt;br /&gt;
                      &lt;div style='padding-top:1%'&gt;&lt;/div&gt;
                      &lt;input type='submit' value='Submit' /&gt;&lt;br /&gt;
                      &lt;/div&gt;
                  &lt;/form&gt;
              &lt;/div&gt;";
  </code></pre>
  
  <hr>
  
  <p>Now I want to enable/disable the text box on the basis of value selected in drop down.</p>
  
  <p>Here i like to put a condition where if the option value equals 'allcaller' the text box should be disabled which is actually happening.
  But I want to enable the same text box in case option value equals to 'specialcaller'.</p>
  
  <p>I wasn't able to enable the text box on the basis of value selected in drop down.</p>
  
  <p>Any help would be highly appreciated.</p>
  
  <p>Thanks! 
  Bobby.</p>