PHP 数组

In this tutorial you'll learn how to store multiple values in a single variable in PHP.

## What is PHP Arrays
Arrays are complex variables that allow us to store more than one value or a group of values under a single variable name. Let's suppose you want to store colors in your PHP script. Storing the colors one by one in a variable could look something like this:

```php
<?php
$color1 = "Red";
$color2 = "Green";
$color3 = "Blue";
?>
```
But what, if you want to store the states or city names of a country in variables and this time this not just three may be hundred. It is quite hard, boring, and bad idea to store each city name in a separate variable. And here array comes into play.

## Types of Arrays in PHP
There are three types of arrays that you can create. These are:

- **Indexed array** — An array with a numeric key.
- **Associative array** — An array where each key has its own specific value.
- **Multidimensional array** — An array containing one or more arrays within itself.

## Indexed Arrays
An indexed or numeric array stores each array element with a numeric index. The following examples shows two ways of creating an indexed array, the easiest way is:

```php
<?php
// Define an indexed array
$colors = array("Red", "Green", "Blue");
?>
```
<div class="callout callout-info mb-3">Note: In an indexed or numeric array, the indexes are automatically assigned and start with 0, and the values can be any data type.</div>

This is equivalent to the following example, in which indexes are assigned manually:

```php
<?php
$colors[0] = "Red"; 
$colors[1] = "Green"; 
$colors[2] = "Blue"; 
?>
```
## Associative Arrays
In an associative array, the keys assigned to values can be arbitrary and user defined strings. In the following example the array uses keys instead of index numbers:

```php
<?php
// Define an associative array
$ages = array("Peter"=>22, "Clark"=>32, "John"=>28);
?>
```
The following example is equivalent to the previous example, but shows a different way of creating associative arrays:

```php
<?php
$ages["Peter"] = "22";
$ages["Clark"] = "32";
$ages["John"] = "28";
?>
```
## Multidimensional Arrays
The multidimensional array is an array in which each element can also be an array and each element in the sub-array can be an array or further contain array within itself and so on. An example of a multidimensional array will look something like this:

```php
<?php
// Define a multidimensional array
$contacts = array(
    array(
        "name" => "Peter Parker",
        "email" => "peterparker@mail.com",
    ),
    array(
        "name" => "Clark Kent",
        "email" => "clarkkent@mail.com",
    ),
    array(
        "name" => "Harry Potter",
        "email" => "harrypotter@mail.com",
    )
);
// Access nested value
echo "Peter Parker's Email-id is: " . $contacts[0]["email"];
?>
```
## Viewing Array Structure and Values
You can see the structure and values of any array by using one of two statements — `var_dump()` or `print_r()`. The `print_r()` statement, however, gives somewhat less information. Consider the following example:

```php
<?php
// Define array
$cities = array("London", "Paris", "New York");
 
// Display the cities array
print_r($cities);
?>
```
The `print_r()` statement gives the following output:

```
Array ( [0] => London [1] => Paris [2] => New York )
```
This output shows the key and the value for each element in the array. To get more information, use the following statement:

```php
<?php
// Define array
$cities = array("London", "Paris", "New York");
 
// Display the cities array
var_dump($cities);
?>
```
This `var_dump()` statement gives the following output:

```
array(3) { [0]=> string(6) "London" [1]=> string(5) "Paris" [2]=> string(8) "New York" }
```
This output shows the data type of each element, such as a string of 6 characters, in addition to the key and value. In the [next chapter](http://www.bixiaguangnian.com/manual/php7/3975.html "next chapter") you will learn how to sort array elements.

You will learn how to loop through the values of an array in the [later chapter](http://www.bixiaguangnian.com/manual/php7/3976.html "later chapter").