A brief analysis of the usage of php arrays (Arrays)-PHP Tutorial-php.cn

A brief analysis of the usage of php arrays (Arrays)

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Release： 2016-07-25 08:57:55

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This article introduces some knowledge about PHP arrays as an introductory reference for learning PHP arrays. I hope it will be helpful to friends who are new to PHP.

1. Definition of php array

PHP array represents a set of related data.

In PHP, use array() to define an array. Example:

<html>
<body>
<?php
$a = array("orange", "apple","peach");
echo $a[0];
?>
</body>
</html>

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Among them, $a = array("orange", "apple", "peach"); defines an array variable with three data.

Separate each value of the array with commas.

The following statement echo $a[0] represents the first value of the output array, which is "orange". Note that the array is base 0, not 1. The value in the square brackets [] of the array variable is called the index key of the array. Array is a one-to-one combination of key-value

The basic unit of an array is elements. Each element consists of a pair of index (key, also called "key") and value (value).

Each value has a corresponding index (key). By specifying the key of the array, we get the corresponding value, such as $a[0].

The array definition method in the previous example is a shorthand way of defining an array. It does not define the key of each value of the array. By default, if the key of each value in the array is not defined, the key starts from 0 and automatically increases by 1 each time.

$a = array("orange", "apple","peach");
$a = array(0=>"orange", 1=>"apple",2=>"peach");

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The above two sentences of code have the same effect. The first sentence does not specify the key of the array, so the system automatically adds a key to each value of the array. The value of the key starts from 0 and increases by 1 each time. The second sentence of code is to give each element of the array when defining the array. The value plus is assigned to the corresponding key.

The way to define a key-value pair in an array is: key=>value. For example, 0=>"orange" means that the key is 0 and the corresponding value is "orange".

Although the writing method of specifying a key is more complicated than not specifying a key, it also gives you the freedom to set the key. You can set the key of each value of the array at will. For example:

<html>
<body>
<?php
$a = array(1=>"orange", 3=>"apple",5=>"peach");
echo $a[1];
?>
</body>
</html>

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In addition, the key of the array can also be represented by a string. Note: Use a string as the key. When specifying the key, add quotation marks. For example:

<html>
<body>
<?php
$a = array("os"=>"Windows XP", "lang"=>"Chinese","sp"=>"Service Pack 3");
echo $a["os"],"<br />";
echo $a["lang"],"<br />";
echo $a["sp"];
?>
</body>
</html>

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Note: key can only be integers and strings.

There is another way to define an array, as in the following example:

$a["os"] ="Windows XP";
$a["lang"] ="Chinese";
$a["sp"]="Service Pack 3";

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The effect is the same as $a = array("os"=>"Windows XP", "lang"=>"Chinese","sp"=>"Service Pack 3");.

Second, modify the array

1, add the syntax of an array element: $array_name[key] = value

2. To delete an array element, use the unset function. The syntax is as follows: unset($array_name[key])

An example of adding and deleting an array element is as follows, where $a["c"] = 300; Indicates adding an array element with key "c" and value 300; unset($a["b"]); Indicates deleting an array element with key "b":

<html>
<body>
<?php
$a = array(a=>100, b=>200,d=>500);
$a["c"] = 300;  
unset($a["b"]);

foreach ($a as $key=> $value)
{
  echo $key.": ".$value."<br />";
}
?>
</body>
</html>

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Output: a: 100 D: 500 c: 300