Page 183 - Beginning PHP 5.3

Chapter 7: Functions
sin(30) = 0.5
cos(30) = 0.866025403784

tan(30) = 0.57735026919
In the real world, variable function calling is often used to dynamically select a function to execute on
the fly, depending on, for example, user input or other external factors. You can also use it to write code
that calls user - created callback functions or event handler functions. (You create callback functions in
Chapter 15 and some event handlers in Chapter 19 .)

Writing Your Own Functions

So far you ’ ve learned that functions are useful beasts that let you encapsulate and reuse code, and
you ’ ve explored how to call functions in PHP. Here ’ s where the fun really begins, as you get to create
your own functions.

Defining a function is really easy — just use the following syntax:
function myFunc() {
// (do stuff here)

}
In other words, you write the word function , followed by the name of the function you want to create,
followed by parentheses. Next, put your function ’ s code between curly brackets ( {} ).

Here ’ s a trivial example:
function hello() {
echo “Hello, world! < br/ > ”;
}

// Displays “Hello, world!”
hello();

As you can see, this script defines a function, hello() , that simply displays the string “ Hello,

world! ” After the function definition, the script calls the hello() function to display the output.
Notice that the code within the hello() function is only run when the function is later called, not
when the function itself is created. Simply creating a function does not run the code within the function;
you have to explicitly call the function in order to run its code.

Defining Parameters

As you know, functions can optionally accept one or more arguments, which are values passed to the
function. To tell PHP that you want your function to accept arguments, you specify one or more
corresponding parameters when you define your function. A parameter is a variable that holds the value
passed to it when the function is called.

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