Array
An array is a data structure that
stores one or more values in a single value. For experienced programmers it is
important to note that PHP's arrays are actually maps (each key is mapped to a
value).
PHP - A Numerically Indexed Array
If this is your first time seeing an
array, then you may not quite understand the concept of an array. Imagine that
you own a business and you want to store the names of all your employees in a
PHP variable. How would you go about this?
It wouldn't make much sense to have
to store each name in its own variable. Instead, it would be nice to store all
the employee names inside of a single variable. This can be done, and we show
you how below.
PHP
Code:
$employee_array[0] = "Bob";
$employee_array[1] = "Sally";
$employee_array[2] = "Charlie";
$employee_array[3] = "Clare";
In the above example we made use of
the key / value structure of an array. The keys were the numbers
we specified in the array and the values were the names of the
employees. Each key of an array represents a value that we can manipulate and
reference. The general form for setting the key of an array equal to a value
is:
- $array[key] = value;
If we wanted to reference the values
that we stored into our array, the following PHP code would get the job done.
Note: As you may have noticed from the above code example, an
array's keys start from 0 and not 1. This is a very common problem for many new
programmers who are used to counting from 1 and lead to "off by 1"
errors. This is just something that will take experience before you are fully
comfortable with it.
PHP
Code:
echo "Two of my employees are "
. $employee_array[0] . " & " .
$employee_array[1];
echo "<br />Two more employees of mine are "
. $employee_array[2] . " & " .
$employee_array[3];
Display:
Two of my employees are Bob &
Sally
Two more employees of mine are Charlie & Clare
Two more employees of mine are Charlie & Clare
PHP arrays are quite useful when
used in conjunction with loops, which we will talk about in a later lesson.
Above we showed an example of an array that made use of integers for the keys
(a numerically indexed array). However, you can also specify a string as the key,
which is referred to as an associative array.
PHP - Associative Arrays
In an associative array a key is
associated with a value. If you wanted to store the salaries of your employees
in an array, a numerically indexed array would not be the best choice. Instead,
we could use the employees names as the keys in our associative array,
and the value would be their respective salary.
PHP
Code:
$salaries["Bob"] = 2000;
$salaries["Sally"] = 4000;
$salaries["Charlie"] = 600;
$salaries["Clare"] = 0;
echo "Bob is being paid - $" .
$salaries["Bob"] . "<br />";
echo "Sally is being paid - $" .
$salaries["Sally"] . "<br />";
echo "Charlie is being paid - $" .
$salaries["Charlie"] . "<br />";
echo "Clare is being paid - $" .
$salaries["Clare"];
Display:
Bob is being paid - $2000
Sally is being paid - $4000
Charlie is being paid - $600
Clare is being paid - $0
Sally is being paid - $4000
Charlie is being paid - $600
Clare is being paid - $0
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