PHP Supports scalar and composite data types. In this article, we will discuss one of the composite types: arrays. An array is a collection of data values ​​organized as an ordered set of key-value pairs.

This article talks about creating an array, adding elements to an array. There are many built-in functions that work with arrays in PHP because arrays are common and useful to use. For example, if you want to send an email to more than one email address, you can store the email addresses in an array and then loop through the array, sending messages to the email address taken from the array.

Indexed and associative arrays

There are two types of arrays in PHP: index and associative. The keys of an indexed array are integers starting from 0. Indexed arrays are used when you require a specific position in the array. Associative arrays behave like two columns of a table. The first column is the key, which is used to access the value (the second column).

PHP internally stores all arrays as associative arrays, so the only difference between associative and indexed arrays is that the keys appear. Some functions are provided primarily for use with indexed arrays, since they assume that your keys are sequential integers starting at 0. In both cases, the keys are unique - that is, you cannot have two elements with the same key, regardless whether the key is a string or an integer.

IN PHP arrays have an internal order of their elements that is independent of keys and values, and there are functions that can be used to traverse arrays based on this internal order.

Defining elements in an array

You can access specific values ​​from an array by using the array name followed by the element key (sometimes called index) in square brackets:

$age["Fred"]; $shows;

The key can be a string or an integer. String values ​​as numbers (without leading zeros) are treated as integers. Thus, $array And $array['3'] refer to the same element, but $array[’03’] refers to another element. Negative numbers can also be used as keys, but they do not specify positions from the end of the array, as in Perl.

It is not necessary to write the key in quotes. For example, $array['Fred'] like $arrat. However, it is considered good style PHP always use quotes. If the index is without quotes, then PHP uses the value of the constant as the index:

Define("index",5); echo $array; // will return $array, not $array["index"];

If you want to substitute a number into the index, you need to do this:

$age["Clone$number"]; // will return, for example $age["Clone5"];

However, do not quote the key in the following case:

// incorrect print "Hello, $person["name"]"; print "Hello, $person["name"]"; // correct print "Hello, $person";

Storing data in arrays

When you try to store a value in an array, the array will be automatically created if it did not exist previously, but when you try to retrieve a value from an array that has not been defined, the array will not be created. For example:

// $addresses is not defined until now echo $addresses; // nothing echo $addresses; // nothing $addresses = " [email protected]"; echo $addresses; // print "Array"

You can use a simple assignment to initialize an array in a program:

$addresses = " [email protected]"; $addresses = " [email protected]"; $addresses = " [email protected]"; // ...

We declared an index array with integer indices starting at 0.

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 construct Array(), which builds an array from its arguments:

$addresses = array(" [email protected]", "[email protected]", "[email protected]");

To create an associative array using Array(), use => symbol separating indices from values:

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

Pay attention to the use of spaces and alignment. We could group the code, but it would be less clear:

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

To create an empty array, you need to call the construct Array() without arguments:

$addresses = Array();

You can specify a starting key in an array and then a list of values. Values ​​are entered into the array, starting with the key and then increasing:

$days = array(1 => "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"); // 2 is Tuesday, 3 is Wednesday, etc.

If the starting index is a string, then subsequent indices become integers, starting at 0. So the following code is probably an error:

$whoops = array("Friday" => "Black", "Brown", "Green"); // same as $whoops = array("Friday" => "Black", 0 => "Brown", 1 => "Green");

Adding a new element to the end of an array

To insert multiple values ​​at the end of an existing indexed array, use the syntax:

$family = array("Fred", "Wilma"); // $family = "Fred" $family = "Pebbles"; // $family = "Pebbles"

This construct assumes that array indices are numbers and assigns the element the next available numeric index, starting at 0. Trying to add an element to an associative array is almost always a programmer error, but PHP will add new elements with numeric indices (starting from 0) without issuing a warning:

$person = array("name" => "Fred"); // $person["name"] = "Fred"; $person = "Wilma"; // $person = "Wilma"

At this stage, we will finish the introductory part of working with arrays in PHP. I look forward to seeing you in the next article.

Adding elements to an array

If the array exists, you can add additional elements to it. This is done directly using the assignment operator (equal sign) in the same way as assigning a value to a string or number. In this case, you don’t have to specify the key of the added element, but in any case, square brackets are required when accessing the array. Adding two new elements to $List, we write:

$List = "pears";
$List = "tomatoes";

If the key is not specified, each element will be added to the existing array and indexed by the next ordinal number. If we add new elements to the array from the previous section, whose elements had indexes 1, 2 and 3, then pears will have index 4, and tomatoes will have index 5. When you explicitly specify an index, and the value with it is already exists, the existing value at that location will be lost and replaced with a new one:

$List = "pears";
$List = "tomatoes";

Now the value of the element with index 4 is “tomatoes”, and the element “oranges” is no longer there. I would advise not to specify a key when adding elements to an array, unless you specifically want to overwrite any existing data. However, if strings are used as indexes, the keys must be specified so as not to lose values.

We will try to add new elements to the array by rewriting the soups.php script. By first printing the original elements of the array, and then the original ones along with the added ones, we can easily see the changes that have occurred. Just as you can find out the length of a string (the number of characters it contains) using the strlen() function, it is also easy to determine the number of elements in an array using the count() function:

$HowMany = count($Array);

1. Open the soups.php file in a text editor.
2. After initializing the array using the array() function, add the following entry:
$HowMany = count($Soups);
print("The array contains $HowMany elements.

\n");

The count() function will determine how many elements are in the $Soups array. By assigning this value to a variable, it can be printed.

3. Add three additional elements to the array.
$Soups["Thursday"] = "Chicken Noodle";
$Soups["Friday"] = "Tomato";
$Soups["Saturday"] = "Cream of Broccoli";
4. Count the elements in the array and print this value.
$HowManyNow = count($Soups);
print("The array now contains $HowManyNow elements.

\n");

5. Save the script (Listing 7.2), upload it to the server and test it in the browser (Fig.).

Listing 7.2 You can directly add one element at a time to an array by assigning a value to each element using the appropriate operator. The count() function can be used to find out how many elements are in an array.

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