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Functions!

We already know what to write when we want to use some PHP code, how to set a variable, and how to print things. Like most languages, PHP also has functions, like rand, which gives us a random number:

<!-- index.php -->
<!-- ... -->

<?php
    $cleverWelcomeMessage = 'All the love, none of the crap!';
    $pupCount = rand();
?>

A function always starts with its name followed by opening and closing parentheses. Those are the key and tell PHP that rand is a function. Think of a function like a machine: we execute it with the code you see here and it returns a value. Not all functions work exactly like this, but most do. So when you see a function, think “this does some work for me and then returns a value.” It might return a number, a string like 'Hello World', or something more complicated.

The rand function returns a random number. We assign that number to the $pupCount variable and then print it just like before with the echo statement.

When we refresh, we see our number is now dynamic: each time we refresh, the rand function gives us another number!

Tip

Generating random numbers is actually kind of tough for computers. Another function, :phpfunction`mt_rand`, generates “better” random numbers.

PHP comes with a lot of built-in functions like rand that you can use immediately. On php.net, you can lookup your function and learn all about it.

Tip

At the time of this recording, php.net was getting a facelift! If you see an older, uglier site, you may see a link at the top of the page to preview the newer site.

Functions with Arguments

Sometimes we can control the behavior of a function by passing it an argument:

<!-- index.php -->
<!-- ... -->

<?php
    $cleverWelcomeMessage = 'All the love, none of the crap!';
    $pupCount = rand(50);
?>

An argument appears between the parentheses of the function and tells the rand function to give us a number that’s 50 or larger. For rand, this argument is optional: the function will work without it and has a default value of 0. I know this by reading its documentation.

Tip

PHP often uses the word “parameter” in place of argument in its documentation and error messages. These two words mean the same thing.

In fact, we can see that rand has 2 arguments: the minimum number and a maximum. To pass a second argument, just add a comma after the first:

<!-- index.php -->
<!-- ... -->

<?php
    $cleverWelcomeMessage = 'All the love, none of the crap!';
    $pupCount = rand(50, 100);
?>

When we refresh, our pup number is random, but between 50 and 100. Functions are machines that do work and return a value. Arguments are input that let us control the function. We pass arguments to the function as a comma-separated list inside its parentheses.

Tip

Functions don’t always return a value. Some functions just do something but return nothing. An example is var_dump, which prints to the screen similar to echo. We’ll see this in a moment.

Capitalizing the first Letter of each Word

Every function has a different number of total arguments that mean different things. Let’s look up a cool function called ucwords. This function has only one argument, but it’s required:

<!-- index.php -->
<!-- ... -->

<?php
    $cleverWelcomeMessage = ucwords('All the love, none of the crap!');
    $pupCount = rand(50, 100);
?>

When we refresh the browser, every word in the string is upper-cased!

All The Love, None Of The Crap!

Since the one argument is required, if we leave it off, PHP will give us a “friendly” reminder:

<!-- index.php -->
<!-- ... -->

<?php
    $cleverWelcomeMessage = ucwords();
    $pupCount = rand(50, 100);
?>
PHP Warning: ucwords() expects exactly 1 parameter, 0 given in /path/to/project/index.php on line 69

The point is that PHP has a lot of functions, and each has different arguments that mean different things. Some arguments are required, like the first and only argument of ucwords and some are optional, like both arguments to rand.

When you need to do something like generate a random number, the best thing to do is google your question, find the function you need, then research it on php.net. Every page has comments below it and a spot where you can learn about similar functions.

Lowercasing all letters / Using Functions in Different Places

Let’s look at one of the related functions strtolower. Like the name suggests, when we give this function its one required argument, it will make every character lowercase and return it. Let’s replace ucwords with this. But instead of using it to set the $cleverWelcomeMessage variable to a lowercase string, we can use it to lowercase the string message just before echo prints it:

<!-- index.php -->
<!-- ... -->

<div class="jumbotron">
    <div class="container">
        <?php
            $cleverWelcomeMessage = 'All the love, none of the crap!';
            $pupCount = rand(50, 100);
        ?>

        <h1><?php echo strtolower($cleverWelcomeMessage); ?></h1>
        <!-- ... -->
    </div>
</div>

Just like your new pup, a function can really go anywhere. And variables can be used as arguments. Remember, $cleverWelcomeMessage represents our string message, so this is the same as passing the string directly (e.g. strtolower('All the love, none of the crap!')).

Let’s get fancy and use another function - strrev - to print the string in reverse:

<h1><?php echo strrev(strtolower($cleverWelcomeMessage)); ?></h1>

When we fresh, our string is all lowercase AND reversed.

<h1>!parc eht fo enon ,evol eht lla</h1>

You can use functions inside of functions like this as much as you want. The trick is to keep track of your parenthesis and always remember to have a closing parenthesis for every opening one.

But what order do things take place? Is the string lowercased and then reversed or reversed first and then lowercased? If we replace strrev with strtoupper, the opposite of strtolower, then it becomes obvious:

<h1><?php echo strtoupper(strtolower($cleverWelcomeMessage)); ?></h1>

When we refresh, the string displays completely in upper case:

<h1>ALL THE LOVE, NONE OF THE CRAP!</h1>

This proves that the string is lowercased first and then uppercased. Functions work from the inside out. Initially cleverWelcomeMessage is passed as the first argument to strtolower and a lowercase string is returned. This lowercase string is then passed as the first argument to strtoupper, which returns an upper case string. Which is finally printed with echo. Phew!

This is all really cool, but if you do feel overwhelmed, you could always write this using multiple lines:

<!-- index.php -->
<!-- ... -->

<div class="jumbotron">
    <div class="container">
        <?php
            $cleverWelcomeMessage = 'All the love, none of the crap!';
            $lowerMessage = strtolower($cleverWelcomeMessage);
            $upperMessage = strtoupper($lowerMessage);
            $pupCount = rand(50, 100);
        ?>

        <h1><?php echo $upperMessage; ?></h1>
        <!-- ... -->
    </div>
</div>

The most important thing to remember is that PHP has a lot of functions, which are always written with a set of parenthesis after their name. Some have one or more arguments that allow you to control the function and the documentation explains these. Functions typically do some work and return a value, which you can assign to variables or print using echo. Got it? Ok, onto practicing with the activities!

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