Storing Data in Arrays

Storing a value in an array will create the array if it didn’t already exist, but trying to retrieve a value from an array that hasn’t been defined yet won’t create the array. For example:

    // $addresses not defined before this point
    echo $addresses[0];                    // prints nothing
    echo $addresses;                       // prints nothing
    $addresses[0] = 'spam@cyberpromo.net';
    echo $addresses;                       // prints "Array"

Using simple assignment to initialize an array in your program leads to code like this:

    $addresses[0] = 'spam@cyberpromo.net';
    $addresses[1] = 'abuse@example.com';
    $addresses[2] = 'root@example.com';
    // ...

That’s an indexed array, with integer indexes beginning at 0. Here’s an associative array:

    $price['Gasket'] = 15.29;
    $price['Wheel']  = 75.25;
    $price['Tire']   = 50.00;
    // ...

An easier way to initialize an array is to use the array( ) construct, which builds an array from its arguments. This builds an indexed array, and the index values (starting at 0) are created automatically:

    $addresses = array('spam@cyberpromo.net', 'abuse@example.com',
                       'root@example.com');

To create an associative array with array( ), use the => symbol to separate indexes from values:

    $price = array('Gasket' => 15.29,
                   'Wheel'  => 75.25,
                   'Tire'   => 50.00);

Notice the use of whitespace and alignment. We could have bunched up the code, but it wouldn’t have been as easy to read:

    $price = array('Gasket'=>15.29,'Wheel'=>75.25,'Tire'=>50.00);

To construct an empty array, pass no arguments to array( ):

 $addresses = array( ); ...

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