Untitled

<html>

<form>
  First Name: <input id="firstname" type="text" name="firstname"><br><br>
  Last Name: <input type="text" name="lastname"><br><br>
  Nickname: <input id="nickname" type="text" name="lastname"><br><br>
  Street Address: <input type="text" name="stradd"><br><br>
  City: <input type="text" name="lastname"><br><br>
  Birthday: <input type="date" name="bday"><br><br>
  Sex:<select>
  <option value="male">Male</option>
  <option value="female">Female</option>
  <option value="other">Other</option>
</select>
  <br><br>First time to attend this conference? <br>
<input type="radio" name="gender" value="yes"> Yes<br>
<input type="radio" name="gender" value="no"> No<br>
<br>At which days will You paricipate in this conference?<br>
<input id="day1" type="checkbox" name="day1" value="saturday"> Saturday<br>
  <input id="day2" type="checkbox" name="day2" value="sunday"> Sunday<br>
<br>Would You like to buy our conference's T-Shirt?
<input id="tocheck" onclick="showPanel()" type="checkbox" name="pplace" value="yes"> Yes<br>
  <p id="hiddenQuestion" style="display: none">Select T-Shirt text:</p>
<select id="hiddenPanel" style="display: none">
</select>
</form>
<script>
function showPanel()
{

 if(document.getElementById("tocheck").checked)
 {
    document.getElementById("hiddenQuestion").style.display = "inline";
    var panel = document.getElementById("hiddenPanel");
    panel.style.display = "inline";
    var option = document.createElement("option");
        option.text = document.getElementById("firstname").value;
        panel.add(option);
        option.text = document.getElementById("nickname").value;
        panel.add(option);


 }
 else
 {
    var panel = document.getElementById("hiddenPanel");
        var option = document.createElement("option");
        panel.remove(0);
        panel.remove(0);
        document.getElementById("hiddenQuestion").style.display = "none";
        panel.style.display = "none";

 }
}
</script>
</html>