Detailed explanation of PHP's definition of arrays and how to create arrays_php skills

Traditionally, an array is defined as a set of elements with certain common characteristics. Common characteristics here include similarity (car model, baseball team, fruit type, etc.) and type (for example, all elements are strings or integers), etc. Each element is distinguished by a special identifier, which is called a key. Note the word tradition in the sentence above, as this definition can now be abandoned and completely unrelated elements can be included in an array structure. PHP goes one step further, and the elements in the array can even be of different types. For example, an array might contain elements such as state names, zip codes, test scores, or playing cards.

Each entity contains two items: the previously mentioned key and value. You can query the key to get its corresponding value. These keys can be numerical keys or associative keys. Numeric keys have no real connection to the value, they are just the position of the value in the array. For example, an array contains the names of fruits in alphabetical order, with key 0 representing apple and key 2 representing pear. Using PHP syntax, the array is as follows:

$fruits = array(
 "0"=>"apple",
 "1"=>"banana"
 "2"=>"pear"
 );

Using array indexing, the first element (apple) can be referenced as follows:

$fruits[0]

PHP’s numeric index group starts at position 0, not 1.

Unlike this, the associated key has a relationship to the value, rather than the value's position in the array. Mapping arrays associatively is particularly convenient when using numeric index values ​​is not feasible. For example, you might want to create an array that maps fruit abbreviations to fruit names, such as AP/apple, BA/banana, and PE/Pear. Using PHP syntax, the array is as follows:

$fruits = array(
 "AP"=>"apple",
 "BA"=>"banana",
 "PE"=>"pear"
 );

You can quote apple as follows:

$fruits["AP"];

You can also create arrays containing arrays, which are called multidimensional arrays. For example, you can use a multidimensional array to store fruit information. Using PHP syntax, the array is as follows:

$fruits = array(
  "apple"=>array(
 "name"=>"apple",
 "color"=>"red"
 ),
 "banana"=>array(
 "name"=>"banana",
 "color"=>"yellow"
 )
);

Then you can quote apple’s color as follows:

$states["apple"]["color"];

This will return the following value:

red

You will naturally want to know how to traverse an array. PHP provides many methods for traversing arrays. Regardless of which method you use, remember that they all rely on a feature called an array pointer. Array pointers are like bookmarks, telling you the array location you are examining. Instead of manipulating array pointers directly, you use built-in language features or functions to iterate over the array. However, it is useful to understand this basic concept.

Arrays are one of the most important data structures in PHP. Arrays are widely used in PHP. Unlike many other languages' array implementations, PHP does not require you to specify the size of an array when you create it. In fact, because PHP is a loosely typed language, you don't even need to declare an array before using it. Although there are no restrictions, PHP still provides formal and informal ways to declare arrays. Both methods have their own advantages and are worth learning. These two methods will be discussed separately below, with the informal method introduced first.

To reference each element in a PHP array, you can use a pair of square brackets to indicate it. Because arrays have no size limit, you can create an array by simply establishing a reference, for example:

$fruits[0] = "apple";

The first element of the array $fruits can then be displayed as follows:

echo $fruits[0] = "apple";

Next, you can add additional values ​​by mapping new values ​​to the array index, as follows:

$fruits[1] = "banana";
$fruits[2] = "pear";

Interestingly, if you think that the index value is an array index and is increasing, you can also omit the index value when creating:

$fruits[] = "apple";
$fruits[] = "banana";
$fruits[] = "pear";

Creating associative arrays this way is also very simple, but you must always use keys. The following example creates an array that maps fruits to their colors:

$fruits["apple"] = "red";
$fruits["banana"] = "yellow";
$fruits["pear"] = "yellow";

Use array() to create an array

The

array() function accepts 0 or more elements as input and returns an array containing these income elements. Its form is as follows:

array array([item1,[,item2…[,itemN]]])

The following is an example of using array() to create an indexed array:

$fruits = array("apple","banana","pear");

You can also use array() to create an associative array, as follows:

$fruits = array(
 "AP"=>"apple",
 "BA"=>"banana",
 "PE"=>"pear"
 );