Drop down multi select and find value

<select name="ddlDomainType" id="ddlDomainType" multiple="True" size="5"  class="dropmenu" runat="server">
     <option>pramod</option>
      <option>suyash</option>
       <option>nitin</option>
            </select>
        <asp:Button ID="Button1" runat="server" Text="Button" onclick="Button1_Click" />


 protected void Button1_Click(object sender, EventArgs e)
    {
        for (int i = 0; i < ddlDomainType.Items.Count; i++)
        {
            if (ddlDomainType.Items[i].Selected == true)
            {
                pp =pp + ddlDomainType.Items[i].Value+",";
            }
        }
        Response.Write(pp);
    }