文本框贼值
<script   language= "javascript ">
<!--
function   add()
{
a=document.getElementById( "aa ").value
b=document.getElementById( "bb ").value
c=a+b
document.getElementById( "cc ").value=c
}
-->
</script>
<form   id= "form1 "   name= "form1 "   method= "post "   action= " ">
    <table   width= "100% "   border= "0 "   cellspacing= "0 "   cellpadding= "0 ">
        <%for   i=1   to   3%>
                <tr>
            <td> <label>
                <input   name= "aa "   type= "text "   id= "aa "   />
            </label> </td>
            <td> <label>
                <input   name= "bb "   type= "text "   id= "bb "   />
            </label> </td>
            <td> <label>
                <input   name= "cc "   type= "text "   id= "cc "     onclick= "add() "     />
            </label> </td>
        </tr>
                <%
                next
                %>
        <tr>
            <td>   </td>
            <td> <label>
                <input   type= "submit "   name= "Submit "   value= "提交 "   />
            </label> </td>
            <td>   </td>
        </tr>
    </table>
</form>
一表单有三个文本框,当第一第二个文本框填写值点击第三个文本框,第三个文本框的值自动等于前两个框的和
当只有一行时是可以的,但是要循环多次就不行了,请高手指点.

------解决方案--------------------
function add()
{
var obj = event.srcElement;
var lista = document.form1.aa;
var listb = document.form1.bb;
var listc = document.form1.cc;
if(listc.length){
for(var i=0;i <listc.length;i++){
if(listc[i]==obj) break;
}
if(i <listc.length){
listc[i].value = lista[i].value + listb[i].value;
}
}
else listc.value = lista.value + listb.value;
}
------解决方案--------------------
<input name= "aa " type= "text " id= "aa " />
<input name= "bb " type= "text " id= "bb " />
<input name= "cc " type= "text " id= "cc " onfocus= "if(document.getElementById( 'aa ').value&&document.getElementById( &