Looks like a good example script, you can implement it on your products results page like this:
line 480
<?php echo $row_WADAProducts["ProductShortDesc"]; ?>
Update it with your code like this:
<?php
$string = "" . $row_WADAProducts['ProductShortDesc'] . "";
$max = 100;
substr($string,0,strpos($string," ",$max));
if(strlen($string) > 100){ echo ". . .";}
?>