我有一个与输入金额直接相关的复选框。 如果有输入金额，则必须在发布前检查复选框

I've created a function for a standard checkbox in php, it's called cbox as well as a standard input box called inp.

<tr><td><?php cbox('charge_cc'); ?> Charge CC? Amount $ <?php inp('charge_amt'); ?></td></tr>

If there is an amount entered into the 'charge_amt' inp field the checkbox needs to be checked as well before they post/submit.

If no amount has been entered into the input field than they do not need to check the box and can proceed to fill out the rest of the form and submit. I'm uncertain on how to accomplish this because i think my php functions for cbox and inp are breaking my jquery/javascript.

As of now i've tried a few variations:

<script type="text/javascript">
function validate(){
if (document.getElementById('charge_cc').checked){
          alert("checked") ;
}else{
alert("You didn't check it! Let me check it for you.")
}
}
</script>

No avail, any help would be greatly appreciated.

<td><input type="hidden" name="charge_cc" value="0" class="charge_cc">
    <input type="checkbox" id="charge_cc" name="charge_cc" value="1" class="charge_cc"> Charge CC? Amount $ <input type="text" id="charge_amt" name="charge_amt" value="" size="8" maxlength="6"></td>

If all you need is to check/uncheck the checkbox depending on an entry in the charge_amt text-input, I'd suggest:

$('#charge_amt').keyup(function(){
    var that = this;
    $('#charge_cc').prop('checked', function(){
        return that.value.length;
    });
});

JS Fiddle demo.

If you want to prevent the user un-checking the checkbox once there's a value in the text-input:

$('#charge_amt').keyup(function () {
    var test = this.value.length;
    $('#charge_cc').prop({
        'checked': test,
            'disabled': test
    });
});

JS Fiddle demo.

use jquery... if you have a checkbox with an id of charge_cc, this should work

if($("#charge_cc").prop("checked")) ...

jsfiddle with your html and alerts: http://jsfiddle.net/kmV9m/

$(function () {
    $('#charge_amt').on('change', function () {
        var amount = $(this).val();
        if (amount.length > 0) {
            $('#charge_cc').prop('checked', 'checked');
        } else {
            $('#charge_cc').prop('checked',false);
        }
    });
})

Using a bit of jQuery here to do the work for you should do the trick.

http://jsfiddle.net/devlshone/2HZFE/