functions.php

Example (built-in): strlen()
This example returns a string length with the use of strlen()
61

Example (built-in): strtoupper()
This example returns a string in all caps with the use of strtoupper()
THIS EXAMPLE RETURNS A STRING IN ALL CAPS WITH THE USE OF STRTOUPPER()

Example (user-defined): fullName()
This example returns a string containing a full name. The full name was created with the use of a user-defined function.
Lauren Rodriguez

Explanation:

Predefined functions are functions that have already been established in PHP. The first two examples are predefined functions. They were called by simply typing the function name (ex strlen()). I did not need to create the function to use it.

User-defined funcitons are functions that have been created by the user. They only exist because a user has created them. In the final example I created a user-defined function that creates a full name from two seperate strings.