by Hubert Chathi.
Don't edit the cron.php. Moodle is designed to be modular, which means that plugins can extend various parts of Moodle, including adding cron tasks. If you've already created a plugin for this feature, you may be able to add your cron task in there. Otherwise, you can put it in /local. Check out the developer documentation for your plugin type, or for local plugins. (Though, beware that most of the documentation is for 2.x and may not apply to 1.9. In particular, 1.9 did not have local plugins -- it only had a single directory.)