====== Optimizing Execution Time ======
  * avoid printf() when echo is all you need
  * avoid recomputing values inside a loop
    * don't do this:<code php>
for($i=0; $i < count($array); $i++) {/* do something */}
</code>
    * instead, do this:<code php>
$num = count($array);
for($i=0; $i < $num; $i++) { /* do something */ }
</code>
  * include only files that you need; split the functions into more files if they are not always used together
  * if using a database, use persistent connections
  * don't use a regular expression when a simple string-manipulation function will do the job; for example, to turn one character into another in a string, use str_replace(), not preg_replace().