PHP user defined functions. Free online PHP and MySQL Web Database Programming Tutorial...

PHP is a very rich language in terms of its fuctions. There are more than 700 built in fuction available in PHP. PHP also allows us to define our own fuctions.In this lesson we will discuss how we can create our own functions.

In simple words a function is a named block of code that can be executed whenever we need, again and again. All functions start with the word "function()". Function names can start with a letter or an underscore but not with a number. The block of code has to be enclosed between { and }.

Example A simple function that prints "Hello World":

<html>
<body>
<?php
function printHW()
{
echo "Hello World";
}
printVar(); //this is how we call functions in PHP
?>
</body>
</html>

The above was a very simple example of a user defined function. The function in above example does not take any argument and does not return a value. We can define a function that takes arguments and returns a value. Consider the following example:

<?php
function func($arg_1, $arg_2, ..., $arg_n)
{
echo "Example function.\n";
return $retVal;
}
?>

PHP also allows functions to be defined inside functions. This is a rare concept and is not found in many programming languages. The following example shows this concept:

<?php
function func() {
function func2() {
echo "I don't exist until func() is called.\n";
}
}
/* We can't call func2() yet since it doesn't exist. */ func();

/* Now we can call func2(), func()'s processesing has made it
accessible. */
func2(); // this is valid now.
?>

PHP also supports recursive functions:

<?php
function recursive($val) {
if ($val < 10) {
echo "$a\n"; recursive($val + 1);
}
}
?>

Next: PHP Defining Functions 2