As we discussed in Chapter 2, PHP supports both scalar and compound data types. In this chapter, we’ll discuss one of the compound types: arrays. An array is a collection of data values organized as an ordered collection of key-value pairs. It may help to think of an array, in loose terms, like an egg carton. Each compartment of an egg carton can hold an egg, but it travels around as one overall container. And, like an egg carton doesn’t have to only contain eggs (you can put anything in there, like rocks, snowballs, four-leaf clovers, or nuts & bolts), so too an array is not limited to one type of data. It can hold strings, integers, Booleans, and so on. Plus, array compartments can also contain other arrays, but more on that later.
This chapter talks about creating an array, adding and removing elements from an array, and looping over the contents of an array. Because arrays are very common and useful, there are many built-in functions that work with them in PHP. For example, if you want to send email to more than one email address, you’ll store the email addresses in an array and then loop through the array, sending the message to the current email address. Also, if you have a form that permits multiple selections, the items the user selected are returned in an array.