From http://www.w3schools.com (Copyright Refsnes Data)

PHP Functions

The real power of PHP comes from its functions.

In PHP - there are more than 700 built-in functions available.

In this tutorial we will show you how to create your own functions.

For a reference and examples of the built-in functions, please visit our PHP Reference.

Create a PHP Function

A function is a block of code that can be executed whenever we need it.

Creating PHP functions:

All functions start with the word "function()"
Name the function - It should be possible to understand what the function does by its name. The name can start with a letter or underscore (not a number)
Add a "{" - The function code starts after the opening curly brace
Insert the function code
Add a "}" - The function is finished by a closing curly brace

A simple function that writes my name when it is called:

<html>
<body>

<?php
function writeMyName()
  {
  echo "Kai Jim Refsnes";
  }

writeMyName();
?>

</body>
</html>

Now we will use the function in a PHP script:

<html>
<body>

<?php
function writeMyName()
  {
  echo "Kai Jim Refsnes";
  }

echo "Hello world!<br />";
echo "My name is ";
writeMyName();
echo ".<br />That's right, ";
writeMyName();
echo " is my name.";
?>

</body>
</html>

The output of the code above will be:

Hello world!
My name is Kai Jim Refsnes.
That's right, Kai Jim Refsnes is my name.

Our first function (writeMyName()) is a very simple function. It only writes a static string.

To add more functionality to a function, we can add parameters. A parameter is just like a variable.

You may have noticed the parentheses after the function name, like: writeMyName(). The parameters are specified inside the parentheses.

The following example will write different first names, but the same last name:

<html>
<body>

<?php
function writeMyName($fname)
  {
  echo $fname . " Refsnes.<br />";
  }

echo "My name is ";
writeMyName("Kai Jim");

echo "My name is ";
writeMyName("Hege");

echo "My name is ";
writeMyName("Stale");
?>

</body>
</html>

The output of the code above will be:

My name is Kai Jim Refsnes.
My name is Hege Refsnes.
My name is Stale Refsnes.

The following function has two parameters:

<html>
<body>

<?php
function writeMyName($fname,$punctuation)
  {
  echo $fname . " Refsnes" . $punctuation . "<br />";
  }

echo "My name is ";
writeMyName("Kai Jim",".");

echo "My name is ";
writeMyName("Hege","!");

echo "My name is ";
writeMyName("Ståle","...");
?>

</body>
</html>

The output of the code above will be:

My name is Kai Jim Refsnes.
My name is Hege Refsnes!
My name is Ståle Refsnes...

Functions can also be used to return values.

<html>
<body>

<?php
function add($x,$y)
  {
  $total = $x + $y;
  return $total;
  }

echo "1 + 16 = " . add(1,16);
?>

</body>
</html>

The output of the code above will be:

1 + 16 = 17