Original string: hello world
Using strtoupper(): HELLO WORLD
Hello, Panther! Welcome to the site.
Functions are like mini-programs inside your code that perform specific tasks. Built-in functions come ready to use and handle common jobs, like changing text case or working with arrays. User-defined functions let you create your own reusable code blocks, making your program cleaner and easier to manage by avoiding repetition. You call a function by its name, give it any needed information, and it returns a result or performs an action.