Bare Basics - Arrays

What is an array?

The concept of arrays are simple. If you create a variable to store a value, it does exactly that, stores a single value. Whether it’s an integer, string or anything in between. An array is basically a variable that can hold multiple values. Arrays have many uses, but that’s a little beyond what we’re looking at in this tutorial, we’re just trying to get to grips with them for now. Let’s look at the basic syntax for an array;

<?php

$my_array[0] = 'Red';
$my_array[1] = 'Green';
$my_array[2] = 'Blue';

?>

Here we’ve created an array that holds three different values, Red, Green and Blue respectively. These values can be referenced by their number, 0-2. An important note is that arrays are typically started from 0, so in our array which holds values 0-2, there are three values. Forgetting to count the 0 as a number in programming is often called a fencepost error (or off-by-one error). The values are accessed in the same way they are set;

<?php

// echo's 'Red and Blue' (without quotes)
echo $my_array[0] . ' and ' . $my_array[2];

?>

Using arrays in this way can have many uses, but let’s say for arguments sake (so we have something to learn) that we want to store the hex values for the colours (or ‘colors’ for those who choose to butcher the english language!), why not? Let’s have a look at two solutions, one is the bad solution using variables that you so often see in newbie projects, one is the better solution using arrays;

<?php

// messy, messy, messy!
$colour_one_name = 'Red';
$colour_one_hex = '#ff0000';
$colour_two_name = 'Green';
$colour_two_hex = '#00ff00';
$colour_three_name = 'Blue';
$colour_three_hex = '#0000ff';

// the better approach
$colours['red'] = '#ff0000';
$colours['green'] = '#00ff00';
$colours['blue'] = '#0000ff'; 

?>

As you can see, the array approach is much tidier and saves a lot of lines of code in comparison to the variable approach. Ok now we’ve learnt the basics of an array, it can hold a number and a value or a key and a value. Well what if we wanted to store something like employee details (how cliche), we’ll need a sort of… array-within-an-array scenario?…

Multi-Dimensional Arrays

Ooooh, doesn’t it sound scary? Have no fear, multi-dimensional arrays, or associative arrays, may have a big name but they’re actually very simple (and even more useful!). So let’s go back to that previous situation of employee records, of course with what we’ve learnt so far we could come up with something that could work…

<?php

$employee_one['name'] = 'Dan Walker';
$employee_one['email'] = 'dan[at]thephpblog[dot]com';
$employee_one['gender'] = 'm';
$employee_one['salary'] = 99999999; // one day....

$employee_two['name'] = 'Joe Bloggs';
$employee_two['email'] = 'joe[at]bloggs[dot]com;
$employee_two['gender'] = 'm';
$employee_two['salary'] = 20000; // one day....

?>

The above works, we’ve created two arrays, one for each employee, and filled it with data using the key and value method we learned about earlier. That’s great, but what if we wanted to create a loop that displayed all our employee names or something? Well then we’d be pretty screwed because they have different names and we’d have to recode everything every time we added a new employee! Not good! But what if we could put a key and value array inside a standard incremental array. Now you’re thinking!

<?php

$employees[0]['name'] = 'Dan Walker';
$employees[0]['email'] = 'dan[at]thephpblog[dot]com';
$employees[0]['gender'] = 'm';
$employees[0]['salary'] = 99999999;

$employees[1]['name'] = 'Joe Bloggs';
$employees[1]['email'] = 'joe[at]bloggs[dot]com';
$employees[1]['gender'] = 'm';
$employees[1]['salary'] = 20000;

?>

Note: Notice that the salary values do not have quotes round them, that’s because they’re integers - arrays can hold different types of data just as a variable can.
Now that my friend is looking a lot cleaner. The logic is simple, $employees[0] now contains another array, as does $employees[1]. Because these arrays are nested within another array, this is where we get the name multi-dimensional array from (as if you hadn’t already guessed that).

Because we’ve done it this way we can now cycle through loops to do stuff, let’s say we want to list all our employee names, this is how we’d do it.

<?php

$employees[0]['name'] = 'Dan Walker';
$employees[0]['email'] = 'dan[at]thephpblog[dot]com';
$employees[0]['gender'] = 'm';
$employees[0]['salary'] = 99999999;

$employees[1]['name'] = 'Joe Bloggs';
$employees[1]['email'] = 'joe[at]bloggs[dot]com';
$employees[1]['gender'] = 'm';
$employees[1]['salary'] = 20000;

for ($i=0; $i<count($employees); $i++)
{
	echo $employees[$i]['name'] . '<br />';
}

?>

Would list the two employee names on different lines. You see if we use count($employees) then it counts how many values are in the top layer of our array, the first brackets. There are 2 values in this array and so the loop loops twice. It’s important to remember we start the loop from 0 because our array starts from 0.

Conclusion

Of course this has just been the basics of arrays, if you’re interested in how we could use an array like our employees one, why not take a look at my PHP MySQL class which stores its results in a multi-dimensional array.

Thanks for reading, questions and comments welcome =]

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