Examples of Built-In Function and User-Defined Function

1. Built-In Function Example: `strlen()`

The length of the pet's name is: 5 characters.

What is a Built-In Function?
PHP provides built-in functions that you can use right away without having to define them.
For example, the `strlen()` function helps you find out how many characters are in a string that is being used.

2. User-Defined Function Example: `greetPet()`

Hello, Buddy! How are you today?

What is a User-Defined Function?
A user-defined function in PHP is a function that you can write yourself to help perform specific tasks that are asked for.
For example, the `greetPet()` function takes a pet's name and then outputs a personalized greeting for them.

How Do Functions Work?
In PHP, functions are blocks of code that helps perform specific tasks like I said above.
You can call a function to help execute its code whenever it is needs.
This helps keep any type of code well organized and reusable. Many coders use functions in their code.