Code more readable if you place your functions in a separate file. Many PHP add-ons that you download off the internet contain functions already placed into the files that you simply include in your PHP program. However, PHP provides four functions that enable you to insert code from other files. They are:
All include and require functions can take a local file or URL as input, but they cannot import a remote file. Require and include functions are similar in their functionality except for the way in which they handle an irretrievable resources.
include and include_once provide a warning if the resources cannot be retrieved and try to continue the execution of program. The require and require_once functions provide stop processing of the particular page if they cannot retrieve the resources.