Problem with php 'for' loop

Hi,

I have a script like so:

<?php
if ($_POST['NC1']=='Prefix') {$NC1 = 'xx';} else $NC1 = $_POST['NC1'];
 if ($_POST['NC2']=='Chart number') {$NC2 = 'xx';} else $NC2 = $_POST['NC2'];
if ($_POST['NC3']=='Suffix') {$NC3 = 'xx';} else $NC3 = $_POST['NC3'];
if ($_POST['NC4']=='International number') {$NC4 = 'xx';} else $NC4 = $_POST['NC4'];
if ($_POST['NC5']=='Class') {$NC5 = 'xx';} else $NC5 = $_POST['NC5'];
if ($_POST['NC6']=='P,PandA,n/a') {$NC6 = 'xx';} else $NC6 = $_POST['NC6'];
if ($_POST['NC7']=='BA folio number') {$NC7 = 'xx';} else $NC7 = $_POST['NC7'];
if ($_POST['NC8']=='ARCS on cd') {$NC8 = 'xx';} else $NC8 = $_POST['NC8'];
if ($_POST['NC9']=='ARCS region') {$NC9 = 'xx';} else $NC9 = $_POST['NC9'];
if ($_POST['NC10']=='Chart title') {$NC10 = 'xx';} else $NC10 = $_POST['NC10'];
...
?>

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But the thing is, I have over 100 lines like those above, so it's up to ($_POST['NC150']), I want to use 'for' loop here to make it easier, but not sure how to do that.
There's 4 'NC's per line, so normally if I replace all the 'NC' with 'for' loop element (e.g. $i), it wouldn't work, because in one line there will be NC1, NC2, NC3, NC4, and next line NC5, NC6 etc.
I want to have each NC to be NC1 in first line, NC2 in second line and so on, basically same as in php code above. I hope it's clear.

Thanks for any help.