PHP Functions

PHP has many 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.
• will not execute immediately when a page loads.
• will be executed by a call to the function.

Create a User Defined Function in PHP

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

function functionName() {
    code to be executed;
 }

Issues:

• A function name can start with a letter or underscore (not a number).
• It also makes sense to 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:

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

writeMsg(); // call the function
?>

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 separate 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:

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

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

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

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

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

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:

<?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);
?>

PHP Functions - Returning values

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

<?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);
?>