How do I set permissions on all directories and files on a Linux system?

To change all the directories to 755 (
drwxr-xr-x):
find /opt/lampp/htdocs -type d -exec chmod 755 {} \;
To change all the files to 644 (
-rw-r--r--):
find /opt/lampp/htdocs -type f -exec chmod 644 {} \;