It’s pretty simple, but some people might not be able to grasp the concept so I’ll try to make things clear for everyone On to the tutorial!

Recap

In our previous tutorial, we learned that functions could have return values or not:

Example 1: last lesson

<?php

// Yodeling doesn't really bring anything but attention.
yodel();

// Encrypts a string then returns the result, known as a hash.
// This function is built-into PHP and is good for security.
$hash = sha1('String');

?>

I wanna make a basic one!

Let’s start with the famous Hello World function, shall we? This function won’t have a return value, we’ll create another function with one in the next page

Let’s try to call a function named hello_world() and see what happens…

Example 2: calling a custom function

<?php

hello_world();

?>

Oops…

Fatal error: Call to undefined function hello_world() in D:\NOVALISTIC\3.0\example.php on line 3

We haven’t introduced PHP to our hello_world() function. It doesn’t know what we want this function to do and we have to guide it. Computers and programs are highly renowned for their ability to only shut up and follow exactly what you tell them to do.

To declare a function, you need to first add a keyword function. Yeah, it sounds really obvious doesn’t it (I’m shouting out to VBScript and Perl, both of which use sub instead of function to declare custom functions)? Next, name your function, add a pair of parentheses ‘()’ and a pair of curly braces ‘{}’, and we’ll call the function immediately after defining it:

Example 3: structure of a function declaration

<?php

function hello_world()
{
}

// Call our function
hello_world();

?>

You don’t have to place the opening curly brace on another line. That’s just my own coding standard (shared by many other developers though) to make code blocks clearer. You could always place your brace on the same line as the first: function hello_world() {.

Calling our function now does nothing. PHP doesn’t spit any errors. That means our function was defined successfully and PHP had absolutely no problem with the job.

But… there’s nothing between the curly braces. Precisely why nothing happens. PHP thinks hello_world() does nothing. Let’s get it to do something, and I think you know what I want this function to do…

Add an echo command between the curly braces like so, and test/refresh ur PHP script.

Example 4: adding an echo command

<?php

// This function just prints 'Hello World!'
function hello_world()
{
    
    echo 'Hello World!';
    
}

// Call our function
hello_world();

?>

Hello World!

If you got exactly that message ‘Hello World!’, then congratulations you’ve just made your first function! But functions don’t have to be limited to echoing simple sentences like that.

Turn over to define another function that returns a value instead.

A function is what you call in your program to tell it to perform a series of smaller actions, like echo(), substr(), mysql_query(), or your very own functions like calculate_age() or bake_cookies() (which we will learn how to create in the next tutorial).

I’ll be explaining some of the most basic PHP default functions you’ll definitely come across in 99.9% (with a 30-day money-back guarantee… wait I’m not a hosting service) of all PHP scripts, then guiding you on basic methods of usage of said functions.

Name me some basic ones

You’ve seen echo(), its brother print() and a couple more. Here are some other functions that you’ll probably come across often:

• str_replace() – searches a big string and replaces a smaller string/pattern inside it with a new one
• define() – defines a constant value; we’ll learn more some other time
• date() – returns a certain date format, of right now or a given time
• htmlspecialchars() – converts all <, > and & in a string to their HTML entities, i.e. &lt;, &gt; and &amp;
• empty() – checks if a variable is empty

We’ll learn more about the above functions in later tutorials, but for now here’s a little, uh, ‘primer’, followed by guides on how to use some other simple functions.

What’s this about language constructs?

You already know echo(). Actually, it’s not really a function, but a language construct, as in a keyword that should be used in a specific way in a PHP statement. Truth is, I can’t quite explain it, but just understand that echo() isn’t exactly a function so you can omit those parentheses:

Example 1: echo() with and without parentheses

<?php

$str = 'Hello world!';
// Both are perfectly fine, but I prefer omitting parentheses.
echo($str);
echo $str;

?>

And yes, print() is a language construct too, as well as control structures like if() (you learned about this in the previous tutorial).

How do I use functions?

Functions can be called or used in a variety of ways, but I’ll just explain some common ones.

The first way, is to just call it by itself:

Example 2: calling a function on its own

<?php

my_lovely_function();
exit;

?>

Such functions usually aren’t intended to have a return value so can be called by themselves, like echo(). A return value is a value that a function spits back to the program after doing its job. For example, if you made a function that squares a number, you want the function to return the result after squaring it.

Example 3: return value

<?php

$num = 6;

// We throw this number in as what programmers call a parameter or an
// argument (don't worry, functions settle THEIR arguments pretty ethically),
// then our function squares it and returns the result for us to finally echo.
$sqr = square($num);

echo $sqr;

?>

Most functions require parentheses wrapped around its arguments (I prefer that term to parameters, dunno why), separated by commas:

Example 4: some arguments

<?php

// Too many arguments? Line breaks help to clear things up.
do_stuff($alpha, 'bravo', $charlie, array(
    'delta' => 'echo', 
    $foxtrot, 
    'golf'
), $hotel);

?>

Functions with return values are just like the different types of data you handle. So you could stick in a function where a data type would go in something like a formula:

Example 5: what return values mean as well

<?php

// Instead of this...
$title = 'I &lt;3 PHP';
$title = htmlspecialchars($title);
$title = "<h2>$title</h2>";
echo $title;

// You can always try this! Remember our concatenating operator?
$title2 = '<h2>' . htmlspecialchars('I &lt;3 PHP') . '</h2>';
echo $title2;

?>

You can even nest functions, i.e. pass functions as arguments!

Example 6: nesting functions

<?php

// Long procedure?
$ingredients = array(
    // I'd list them but it'd make this snippet too long!
);
$pasta = prepare('pasta', $ingredients);
$g = garnish('spinach');
$dish = serve($pasta, 'hot', $g);

// Though the above is a bit more organized, give this a
// whirl if you find such long code a hassle.
$dish = serve(prepare('pasta', array(/* Your ingredients */)), 'hot', garnish('spinach'));

?>

Well, that’s it for the basics of functions in PHP. I hope you learned something from this tutorial

I heard I can make my own functions!

Like most other programming languages, PHP lets you define your own functions to fulfill your own tasks your way!

You will learn how to create functions in my next PHP post. Stick around