asp.net - conversion to DateTime -

i have following tags select date first day,second month , third year

<select id="d" class="styledselect-day" tabindex="6">                     <option value="">dd</option>                     <option value="1">1</option>                     <option value="2">2</option>                     <option value="3">3</option>                     <option value="4">4</option>                     <option value="5">5</option>                     <option value="6">6</option>                     <option value="7">7</option>                     <option value="8">8</option>                     <option value="9">9</option>                     <option value="10">10</option>                     <option value="11">11</option>                     <option value="12">12</option>                     <option value="13">13</option>                     <option value="14">14</option>                     <option value="15">15</option>                     <option value="16">16</option>                     <option value="17">17</option>                     <option value="18">18</option>                     <option value="19">19</option>                     <option value="20">20</option>                     <option value="21">21</option>                     <option value="22">22</option>                     <option value="23">23</option>                     <option value="24">24</option>                     <option value="25">25</option>                     <option value="26">26</option>                     <option value="27">27</option>                     <option value="28">28</option>                     <option value="29">29</option>                     <option value="30">30</option>                     <option value="31">31</option>                 </select> <select id="m" class="styledselect-month" tabindex="7" >                         <option value="">mm</option>                         <option value="1">jan</option>                         <option value="2">feb</option>                         <option value="3">mar</option>                         <option value="4">apr</option>                         <option value="5">may</option>                         <option value="6">jun</option>                         <option value="7">jul</option>                         <option value="8">aug</option>                         <option value="9">sep</option>                         <option value="10">oct</option>                         <option value="11">nov</option>                         <option value="12">dec</option>                     </select>  <select  id="y"  class="styledselect-year" tabindex="8"> <option value="yyyy">yyyy</option> <option value="2005">2005</option> <option value="2006">2006</option> <option value="2007">2007</option><option value="2008">2008</option><option value="2009">2009</option><option value="2010">2010</option><option value="2011">2011</option><option value="2012">2012</option>                     </select> 

and following js code, using sending information controller. storing these information in session

$.ajax({                         type: "post",                         url: "@url.action("acceptpersonalinfo","register")",                         data: { dateday: $("#d").val(), datemonth: $("#m").val(), dateyear: $("#y").val() },                         success: function () {                             $("#contentspan").load("/register/contactinfo");                         }                      }); 

following session code

public void acceptpersonalinfo(string dateday, string datemonth, string dateyear) //         {             session["dateday"] = dateday;             session["datemonth"] = datemonth;             session["dateyear"] = dateyear;          } 

then have store date in datetime object save databse.

p.dob = convert.todatetime(convert.toint32(session["datemonth"]) + convert.toint32(session["dateday"]) + convert.toint32(session["dateyear"])); 

but not converting datetime. "p.dob" of datetime type. pls why conversion failed.

actually adding integers thats why not getting. try below code

 string date = session["datemonth"].tostring() + "-" + session["dateday"] + "-" + session["dateyear"];  p.dob=convert.todatetime(date);