Looping Through Forms: Best Practice

I am looking for advice on what is "best practice" regarding looping
through a form to check its checkboxes and associated data fields.

Here is what I am trying to do (Here is the page I am working on:
http://www3.telus.net/thothworks/LinLeastSqPoly4.html).
I provide a form for a user to enter up to twenty (M = 20) data pairs.
The user need not enter data for all twenty pairs, but
the user must indicate that data is present by checking the checkbox
beside each valid pair.

If a checkbox is checked, two things happen:

i) a counter, numRows, is incremented to keep track of the total
number of valid pairs entered.

ii) the associated two data values (being x and y) are checked to
ensure that they are valid numbers and, if so, are entered in an array
for use later.

Previously, my forms were small, and I was able to examine each
checkbox of a form individually:
"if (checkbox1.checked) do action A;
if (checkbox2.checked) do action B;
if (checkbox3.checked) do action C;
etc."

However, now that my form has twenty checkboxes, and may get bigger, I
would like to learn how to accomplish this task with a concise loop.
Following is my first attempt and it seems to work. If anyone can
suggest improvements for this code ....