A function is just a section of code that can executed whenever and where you want it to be. The great thing about functions, is that you can use them over and over! It's great because once you create a function that you use more than once, it saves you time on more coding.
You can create your own function, or use one of the hundreds built in functions that PHP offers. You should also know that functions can confusing, and understanding them at first can be difficult for some people. If you're one of those people who ends up having a hard time understanding functions, just keep trying!
This class is long and has a lot of code in it - don't be intimidated by it, I try my best to keep it simple!

Creating your own function:
It's pretty simple to create a function. Here's the syntax:

<?

function functionName()
{
    // code you want to use
}

?>

There are a few basic rules we should go over first. Your PHP functions should be named after what it does. It's much easier to keep track of which function does what if you use this method. And like a variable, it must start with a letter or underscore.
Let's go over the function syntax real quick:
To define a function, you must start your block of code with the word "function" and this will tell PHP, "This is a function I'm creating". Then you name your function, followed by (). Everything from your function will go inside the curly brackets. You can even call other functions inside a function!
Note: PHP's recursion is not very good, so if you try to make a function loop through itself ten thousand times.. There's a chance it won't.

Output:
This is something more tutorials and people won't tell you about PHP functions. There are 2 kinds of output:
Output that is created inside the function, and
Output that has to be called from outside the function.

Let's create out first function that outputs a string from inside the function.

<?

function favCar()
{
    echo "Audi";
}

?>

Ok, simple enough. Now let's see how we call it:

<?

echo "I really like ";
favCar();

?>

Displays:

I really like Audi

But what if we added favCar() into what we echo, like so:
<?="I really like " . favCar(); // Remember the shorthand way to echo? ?>
Displays:
AudiI really Like

That's a little backwards.. The reason why our script put "Audi" in front, was because it is trying to be echo'd inside an echo. PHP saw that code like this:
<? echo "I really like " . echo "Audi"; ?>

To remedy this, we use the return command instead of echo inside of our function.

<?

function favCar()
{
    return "Audi";
}

?>

What the return command does is shoot out the answer, and then you can use it inline with a echo command. Think of return like the answer to a solution; 1 + 1 = return.
If this doesn't make any sense to you now, it probably will a little ways down the PHP Learning Road.

Parameters:
A parameter is an extra piece of information that you can feed to your function. The syntax is very similar, only now we add variables inside our regular brackets.

<?

function favCar($name)
{
    echo "My favorite car is " . $name;
}

?>

How to call it:

<?

favCar("Audi"); // Displays "My favorite car is Audi"

?>

$name in the function favCar is a variable, but when we call it, we used a string, which works as well. If we wanted to, we could use a variable rather than a string.

<?

$car = "Audi";
function favCar($name)
{
    echo "My favorite car is " . $name;
}
favCar($car); // Displays "My favorite car is Audi"; same result

?>

Functions can hold many parameters, but we're only going to use two in our next example.

<?

function add($a, $b)
{
    $answer = $a + $b;
    return $answer;

    /* Our we can use
    return $a + $b;
    as a shorter method, your choice! */
}
echo "10 + 5 = " . add(10, 5);

?>

All we did was add a comma after our first parameter, and added another parameter (that looks like a variable).
Our function called add will simply add the first number and the scond number together.
The return shoots out the $answer for $a + $b, and we display it on our page using the echo command.

Boolean:
Boolean logic is a form of algebra that returns TRUE or FALSE. (1 or 0). Don't worry, we don't do algebra in this course!
If something returns 1, it's TRUE. Or if it returns TRUE, it's 1. Same concept with FALSE.
If something returns 0, it's FALSE. Or if it returns FALSE, it's 0.

Let's look at how we fit this in with functions:

<?

function overTen($a, $b)
{
    $total = $a + $b;
    if($total>=10)
    {
        return true;
    }
    else
    {
        return false;
    }
}

if(overTen(5, 5)==true)
{
    echo "Our addition function said our result is equal to or greater than 10";
}
else
{
    echo "Our function's result was below 10";
}

?>

Don't panic! It's not as much code as you think it is. When we break down our code, it looks like this:
A function, and an if/else statement.
In our function, we created a variable that holds the answer to our two parameters.
It also has an if/else statement saying "If the answer is equal to or greater ten, return true. If it is else than 10, return false".
That's the entire function!

The if statement says this:
"If our function overTen() returns true, say '....'. But if it returns false, then say '....'"

So really, you already knew all the parts to that big chunk of code.

Once more, if any of this confuses you, please do not get frustrated (which all programmers do eventually) and quit. This is a major building block for your coding future, and a big help with other computer languages.

Your task:
Create a function that will echo "Hello world" from within itself.
Then create a function that will echo "Hello world", but needs to be echo'd outside of the function.
Then create a function that accepts 2 parameters and adds them together, returning your answer and displaying it.
Finally, create a boolean function that returns true of false, and use an if statement to echo different text on your page.

Once you finish all 4 tasks, you are officially able to write, understand, and use functions! Congratulations!