Learning PHP 101 – Custom Functions

Although PHP has a lot of built in functions. Developers often need to write their own functions in order to achieve their objectives. Functions are useful for eliminating repetition, but they can also be used to perform complex tasks and can even be used to group together a series of functions to output a particular result.

Syntax

function name(arguments) {
    // code to be executed
}

• The keyword function tells PHP that the code following it will be a user defined or custom function.
• name is the name of the function and is not case sensitive. A function name can contain numbers, letter, underscores or dashes.
• The arguments, also known as parameters are optional inputs that allow you to feed information into the function.
• Finally inside the curly braces {} you have your block of code to be executed.

Take a look at the following function:

<?php
    // our user defined function
    function person($name) {
        echo "<p>Name: $name</p>";
    }
    // parameters to pass to the function
    $name = "Matthew";
    // calling our function
    person($name); // Name: Matthew
?>

The function called person has a single argument $name. When calling this function we pass the argument and the function will echo out the code block.

Sometimes we need to return the output of a function rather than echo or print it and to do that we use the return keyword.

The difference between return and echo or print is that return does not display the ouput. That makes it useful for helper functions that process information and return a certain output.

<?php
    // our user defined function
    function person($name) {
        return "<p>Name: $name</p>";
    }
    // parameters to pass to the function
    $name = "Matthew";
    // calling our function
    person($name); // returns <p>Name: Matthew</p>
?>

In order to see what a function returns you can always assign the function to a variable and use var_dump();

<?php
    // calling our function
    $var = person($name); // returns <p>Name: Matthew</p>
    var_dump($var);
?>

In our console that would display:

string(20) "<p>Name: Matthew</p>"

Arguments and Parameters

In our example above we added an argument that allows a function to take some kind of input. A function can accept as many arguments as you need but you should try to keep your functions simple and easy to understand.

<?php
    // our user defined function
    function person($fname, $lname) {
        echo
            "<p>First name: $fname</p>n".
            "<p>Last name: $lname</p>n";
    }
?>

Here we have a function that accepts more than one parameter, $fname and $lname.

If we tried to call person() without inputting all of the parameters it will return a notice for each undefined variable similar to this:

What this tells us is that we have not provided the function with the required arguments and therefor the variable is undefined. i.e. it doesn’t exist!

To overcome this issue we can set some default values for each variable or set them to false.

<?php
    // our user defined function
    function person($fname = false, $lname = false) {
        echo
            "<p>First name: $fname</p>n".
            "<p>Last name: $lname</p>n";
    }
    person();
?>

Now when we call this function it will echo everything in the code block minus the actual values (because we didn’t define any) like this:

First name:
Last name:

Once we pass some arguments.

person("Matthew", "Horne");

We will get the desired outcome like so:

First name: Matthew
Last name: Horne

Avoiding Pointless Output

As mentioned above, when we don’t provide any information to a function, it will still output the rest of the code block. This is not desirable because nothing should output if it has no value.

To overcome this problem we can use an if statement that acts like a gatekeeper:

<?php
    // our user defined function
    function person($fname = false, $lname = false) {
        // gatekeeper
        if(empty($fname) && empty($lname)) return;
        // output
        echo
            "<p>First name: $fname</p>n" .
            "<p>Last name: $lname</p>n";
    }
    person();
?>

Now when we try to call the function person() without any parameters it will not echo any output, instead it will return NULL.

Function-ception

Functions can be called within functions and this is where functions that return their output are most useful. Functions that echo output are usually intended to be visible in the browser whereas as functions that return their output are usually intended to pass their output for further use.

<?php            
    // our user defined function
    function person($fname = false, $lname = false) {
        // gatekeeper
        if(empty($fname) && empty($lname)) return;
        // output
        echo
            "<p>Welcome " . format_name($fname). " " . format_name($lname) . ".</p>n";
    }
    // helper function that returns its output
    function format_name($string) {
        // note the order
        return ucfirst(strtolower($string));
    }
    person("mattHew", "hoRNe");            
?>

In this example we have two functions. The first function person() provides us with the output that will be visible to the user. The other function format_name() is a helper function that returns its output after processing.

Notice that the helper function uses two built in PHP functions; ucfirst() and strtolower() which help to correct formatting errors when a user enters their name.

The order of these two function is important; if the order was:

strtolower(ucfirst($string));

The  the output would first convert the first character to uppercase and then convert the whole string to lowercase which is not what we want. So ensure you take note of the order in which functions are called. A rule of thumb would be start from the inner most function and work your way out.

Summarize

By now you should have a good overview of the fundamentals of PHP. It is important that you can properly comprehend the basics as it will lay down a solid foundation for learning some of the more advanced aspects of PHP.