THE WORLD'S LARGEST WEB DEVELOPER SITE

PHP Tutorial

PHP HOME PHP Intro PHP Install PHP Syntax PHP Comments PHP Variables PHP Echo / Print PHP Data Types PHP Strings PHP Numbers PHP Constants PHP Operators PHP If...Else...Elseif PHP Switch PHP While Loops PHP For Loops PHP Functions PHP Arrays PHP Sorting Arrays PHP Superglobals

PHP Forms

PHP Form Handling PHP Form Validation PHP Form Required PHP Form URL/E-mail PHP Form Complete

PHP Advanced

PHP Arrays Multi PHP Date and Time PHP Include PHP File Handling PHP File Open/Read PHP File Create/Write PHP File Upload PHP Cookies PHP Sessions PHP Filters PHP Filters Advanced

MySQL Database

MySQL Database MySQL Connect MySQL Create DB MySQL Create Table MySQL Insert Data MySQL Get Last ID MySQL Insert Multiple MySQL Prepared MySQL Select Data MySQL Delete Data MySQL Update Data MySQL Limit Data

PHP XML

PHP XML Parsers PHP SimpleXML Parser PHP SimpleXML - Get PHP XML Expat PHP XML DOM

PHP - AJAX

AJAX Intro AJAX PHP AJAX Database AJAX XML AJAX Live Search AJAX Poll

PHP Examples

PHP Examples PHP Quiz PHP Exercises PHP Certificate

PHP Reference

PHP Overview PHP Array PHP Calendar PHP Date PHP Directory PHP Error PHP Filesystem PHP Filter PHP FTP PHP Libxml PHP Mail PHP Math PHP Misc PHP MySQLi PHP Network PHP SimpleXML PHP Stream PHP String PHP XML Parser PHP Zip PHP Timezones

PHP Functions


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


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.


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 followed by brackets ():

Example

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

writeMsg(); // call the function
?>
Try it Yourself »


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:

Example

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

familyName("Jani");
familyName("Hege");
familyName("Stale");
familyName("Kai Jim");
familyName("Borge");
?>
Try it Yourself »

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");
?>
Try it Yourself »

PHP is a Loosely Typed Language

In the example above, notice that we did not have to tell PHP which data type the variable is.

PHP automatically associates a data type to the variable, depending on its value. Since the data types are not set in a strict sense, you can do things like adding a string to an integer without causing an error.

In PHP 7, type declarations were added. This gives us an option to specify the data type expected when declaring a function, and by enabling the strict requirement, it will throw a "Fatal Error" on a type mismatch.

In the following example we try to add a number and a string without the strict requirement:

Example

<?php
function addNumbers(int $a, int $b) {
    return $a + $b;
}
echo addNumbers(5, "5 days");
// since strict is NOT enabled "5 days" is changed to int(5), and it will return 10
?>
Try it Yourself »

In the following example we try to add a number and a string with the strict requirement:

Example

<?php declare(strict_types=1); // strict requirement

function addNumbers(int $a, int $b) {
    return $a + $b;
}
echo addNumbers(5, "5 days");
// since strict is enabled and "5 days" is not an integer, an error will be thrown
?>
Try it Yourself »

To specify strict we need to set declare(strict_types=1);. This must be on the very first line of the PHP file. Declaring strict specifies that function calls made in that file must strictly adhere to the specified data types

The strict declaration can make code easier to read, and it forces things to be used in the intended way.

Going forward in this tutorial, we will use the strict requirement.


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 declare(strict_types=1); // strict requirement
function setHeight(int $minheight = 50) {
    echo "The height is : $minheight <br>";
}

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

PHP Functions - Returning values

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

Example

<?php declare(strict_types=1); // strict requirement
function sum(int $x, int $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);
?>
Try it Yourself »

PHP Return Type Declarations

PHP 7 also supports Type Declarations for the return statement. Like with the type declaration for function arguments, by enabling the strict requirement, it will throw a "Fatal Error" on a type mismatch.

To declare a type for the function return, add a colon ( : ) and the type right before the opening curly ( { )bracket when declaring the function.

In the following example we specify the return type for the function:

Example

<?php declare(strict_types=1); // strict requirement
function addNumbers(float $a, float $b) : float {
    return $a + $b;
}
echo addNumbers(1.2, 5.2);
?>
Try it Yourself »

You can specify a different return type, than the argument types, but make sure the return is the correct type:

Example

<?php declare(strict_types=1); // strict requirement
function addNumbers(float $a, float $b) : int {
    return (int)($a + $b);
}
echo addNumbers(1.2, 5.2);
?>
Try it Yourself »

PHP Exercises

Test Yourself With Exercises

Exercise:

Create a function named myFunction.

 {
  echo "Hello World!";
}