// The code above will throw an error, I believe you meant to
// echo number_format($mynum) instead of $mynumstr
// variable $mynum holds the value of the string processed by
// doubleval
<?php
$mynumstr = "100,000,000.75";
$mynum = doubleval(str_replace(",","",$mynumstr));
echo "Normal Value:".number_format($mynum);
?>