Running sum of textboxes w for loop

Hi,
Have an example with an orderform for two products. The form has columns of textboxes. Split in a lot of sections (showing the first two as an example) These textboxes are then sent to a PHP script. But I want to validate that the form is correct first. The textboxes are named as

<form action=”process.php” method=”post”>
<tr>
<td> input name=”Amount1[]” id=”Amount1[]” />
<td> input name=”Amount2[]” id=”Amount2[]” />
</tr>

<tr>
<td> input name=”Amount1[]” id=”Amount1[]” />
<td> input name=”Amount2[]” id=”Amount2[]” />
</tr>

…

…

In the last section I have two textboxes “sum_amount1” and “sum_amount2”. Basically I want to add up all amount1[] boxes into sum_amount1. Not using textbox1 + textbox2 etc. but instead using a for loop.

Some expert coders around to help me?

Thanks in advance.

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