jQuery accessing form array

I have a php form and I want to display or hide certain fields dependant on what I select in a drop down. I have code below which works:

$(document).ready(function() {
    $('div.pupname').hide();
    $('div.pupnid').hide();

    if ($("#perpetrator").val == "1") {
        $('div.pupname').hide();
        $('div.pupid').show();
        else {
            $('div.pupid').hide();
            $('div.pupname').show();
        }

        $("#perpetrator").change(function() {
            if ($("#perpetrator").val() == "1") {
                $('div.pupname').hide();
                $('div.pupid').show();
                else {
                    $('div.pupid').hide();
                    $('div.pupname').show();
                }
            });

        });

I now want to have a multi row block which I am generating using php so I can generate the divs as pupid1, pupid2 etc. and the field $m_perpetrator as an array. I've tried a few ways of accessing the array but can't get anything to work. I thought he following might be along the correct lines for accessing the elements of the array but it does nothing.

if ($("#m_perpetrator[1]").val == "1") {
    $('div.pupname1').show();
    $('div.pupid1').hide();
}
else {
    $('div.pupid1').show();
    $('div.pupname1').hide();
}

Added

Here is a snippet of the HTML

<td><select name="m_perpetrator[1]" id="m_pe开发者_如何学Gorpetrator[1]">
<option value="1">Current</option>
<option value="2" selected>Former</option>
<option value="3">Parent/Carer</option>
</select>
</td> 
<td>Name</td>
<td>
<div class="pupname1">
<input type="text" size=60 name="m_pupil_name[1]" value="JOHN SMITH">
</div>

<div class="pupid1">
<select name="m_pupil_id[1]"  onchange="getXtras(this)">
<option value="">Select .....</option>

So basically this is a multi row form and on each row if Current is selected then I want to display pupil_id if anything else is selected then I want to display pupil name. For processing the input I run round the array m_perpetrator[] using php Jim

Not completely sure what you need. Do you have multiple elements with the same id m_perpetrator?

Use class instead you should do it this way

if ($($(".m_perpetrator")[1]).val() == "1") {
    $('div.pupname1').show();
    $('div.pupid1').hide();
}
else {
    $('div.pupid1').show();
    $('div.pupname1').hide();
}

Otherwise what is m_perpetrator in html?

You can't use "[" or "]" in the id attribute. I'd suggest you output a list element like this:

<ul id="whatevers">
    <li><input name="whatever1" /></li>
    <li><input name="whatever2" /></li>
    <li><input name="whatever3" /></li>
<ul>

You can then access them with jquery like this:

var ws = $("#whatevers input");
for(var i=0; i< ws.length; ++i){
    ws.eq(i).doSomething();
}