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Learning PHP and MySQL by Jon A. Phillips, Michele E. Davis

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Chapter 5. Functions

To write programs in PHP that contain more than just a couple of pages of code and are still organized enough to be useful, you need to understand functions. Functions provide a way to eliminate repeating the same lines of code over and over in your programs. Functions work by assigning a name to a chunk of code, called a function name. Then you execute the code by calling that name.

There are hundreds of built-in functions in PHP. For example, print_r is a function that prints readable information about a variable in plain English rather than code.

If given a string, integer, or float, the value itself is printed with the print_r function. If given an array, values are shown as keys and elements. A similar format is used for objects. With the advent of PHP 5.0, print_r and var_export show protected and private properties of objects.

Functions run the gamut from aggregate_info to imap_ping through pdf_open_image. Since there are so many, we can only cover some basics in this chapter, but we'll give you enough information that you'll be using functions like a pro in no time at all. You can search http://www.php.net for an exhaustive list of functions.

Specifically, we'll go over the following:

  • How to create a function, give it a name, and execute that function

  • How to send values to a function and use them in the function

  • How to return values from a function and use them in your code

  • How to verify a function exists before you try using it

When to split out code into a ...

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