PHP 5 Functions

The real power of PHP comes from its functions; it has more than 1000 built-in functions.

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PHP User Defined Functions

Besides the built-in PHP functions, we can create our own functions.
A function is a block of statements that can be used repeatedly in a program.
A function will not execute immediately when a page loads.
A function will be executed by a call to the function.

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Create a User Defined Function in PHP

A user defined function declaration starts with the word "function":

Syntax

function functionName() {
  code to be executed;
}

Note: A function name can start with a letter or underscore (not a number).
Tip: Give the function a name that reflects what the function does!

	Function names are NOT case-sensitive.

In the example below, we create a function named "writeMsg()". The opening curly brace ( { ) indicates the beginning of the function code and the closing curly brace ( } ) indicates the end of the function. The function outputs "Hello world!". To call the function, just write its name:

Example

<?php
function writeMsg() {
  echo "Hello world!";
}

writeMsg(); // call the function
?>

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PHP Function Arguments

Information can be passed to functions through arguments. An argument is just like a variable.
Arguments are specified after the function name, inside the parentheses. You can add as many arguments as you want, just seperate them with a comma.
The following example has a function with one argument ($fname). When the familyName() function is called, we also pass along a name (e.g. Jani), and the name is used inside the function, which outputs several different first names, but an equal last name:

Example

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

familyName("Jani");
familyName("Hege");
familyName("Stale");
familyName("Kai Jim");
familyName("Borge");
?>

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The following example has a function with two arguments ($fname and $year):

Example

<?php
function familyName($fname,$year) {
  echo "$fname Refsnes. Born in $year <br>";
}

familyName("Hege","1975");
familyName("Stale","1978");
familyName("Kai Jim","1983");
?>

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PHP Default Argument Value

The following example shows how to use a default parameter. If we call the function setHeight() without arguments it takes the default value as argument:

Example

<?php
function setHeight($minheight=50) {
  echo "The height is : $minheight <br>";
}

setHeight(350);
setHeight(); // will use the default value of 50
setHeight(135);
setHeight(80);
?>

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PHP Functions - Returning values

To let a function return a value, use the return statement:

Example

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

echo "5 + 10 = " . sum(5,10) . "<br>";
echo "7 + 13 = " . sum(7,13) . "<br>";
echo "2 + 4 = " . sum(2,4);
?>

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