一个添加值班表的问题？ - 编程论坛

请高手帮忙看看，为什么添加的值班表总是天数不对？不知道应该怎么改？

程序代码：

<%
function zhuanghu(yea,mon)
dat1=yea&"-"&mon&"-1"
dat=datepart("d",dateadd("d",-1,dat1))
zhuanghu=dat
end function
%>
<%
'变量定义
dim action,classid,id,url,pic
action    =    trim(request.querystring("action"))
classid    =    trim(request.QueryString("classid"))
id        =    trim(request.QueryString("id"))
url     =   request.servervariables("http_referer")

%>

<%
'循环开始
select case action
'//推荐
case "add"
%>
<form action="?action=addok" method="post" name="form" id="form">
<table width="100%" border="0" cellspacing="1" cellpadding="0" align="center">
<tr>
<th colspan=8 style="text-align:center;">添加值班人员</th>
</tr>
<%
dim y,m,i
set rs=server.CreateObject("adodb.recordset")
    rs.open "select top 1 * from zhiban  order by id desc ",conn,1,3
     y=rs("y")
    m=rs("m")
    rs.Close
    set rs=nothing
    if m=12 then
    y=y+1
    m=1
    else
    m=m+1
    end if
    t=zhuanghu(y,m)

    for  i=1 to t  Step 1
%>
<tr>
<td width="96" height=30 >值班时间
<%if i=1 then %>
<input name="HIde" type="hidden" value="<%=t%>">
<input name="y" type="hidden" value="<%=y%>">
<input name="m" type="hidden" value="<%=m%>">
<%end if%>
</td>
<td width="89"><input name="date<%=i%>" type="text" id="date<%=i%>" size="10"  value="<%=y&"-"&m&"-"&i%>"></td>
<td width="145" >带班领导</td>
<td width="198" ><input name="lingdao<%=i%>" type="text" id="lingdao<%=i%>" size="30" value=""></td>
<td width="153" >值班人员</td>
<td width="188" ><input name="yuangong<%=i%>" type="text" id="yuangong<%=i%>" size="30" value=""></td>
<td width="149" >值班电话</td>
<td width="223" >
<input name="siji<%=i%>" type="text" id="siji<%=i%>" size="30" value=""></td>
</tr>
<%
Next
%>
<tr>
  <td width="96" height=24 >　</td>
  <td width="89" >　</td>
  <td width="145" class="td2">　</td>
  <td width="198" class="td2">　</td>
  <td width="153" class="td2">　</td>
  <td width="188" class="td2">　</td>
  <td width="149" class="td2">　</td>
  <td width="223" class="td2">
    <input type="submit" value="提交" name="B1">   <input type="reset" value="重置" name="B2"></td>
</tr>
</table>
</form>