Chapter 5. ARRAYS

Single-Dimensional Arrays.............................................................................

Indexing Arrays...................................................................................................

Initializing Arrays...............................................................................................

Multidimensional Arrays..................................................................................

Casting Arrays.....................................................................................................

Referencing Arrays Inside Strings

Arrays collect values into lists. You refer to an element in an array using an index, which
is often an integer but can also be a string. And the value of the element can be text, a
number, or even another array. When you build arrays of arrays, you get
multidimensional arrays. Arrays are used extensively by PHP's built-in functions, and
coding would be nearly impossible without them. There are many functions designed
simply for manipulating arrays. They are discussed in detail in Chapter 9.

Single-Dimensional Arrays

To refer to an element of an array, you use square brackets. Inside the brackets you put
the index of the element, as in Listing 5.1. This construct may be treated exactly like a
variable. You may assign a value or pass its value to a function. You do not have to
declare anything about the array before you use it. Like variables, any element of an array
will be created on the fly. If you refer to an array element that does not exist, it will
evaluate to be zero or an empty string depending on the context.

Single-dimensional arrays are lists of values under a common name. But you might
wonder, "Why bother?" You could just as easily create variables like "$Cities1,
$Cities2, $Cities3" and not worry about square brackets. One reason is that it's easy
to loop through all values of an array. If you know that all the elements of an array have
been added using consecutive numbers, you can use a for loop to get each element. PHP
makes it easy to create arrays that work this way; if you leave out an index when
assigning an array element, PHP will start at zero and use consecutive integers thereafter.
If you run the code in Listing 5.2, you will discover that the four cities have indexes of 0,
1, 2, and 3.

Listing 5.1 Referencing Array Elements