There are several ways to define arrays in php

php has five ways to define arrays, which are: 1. Use array to create an array; 2. Use "$arr[] = 'a';" to create an array; 3. Use "array(1 =>'jack',2=>'lucy',500=>'hcoder')" to create an array; 4. Use "$arr[1] = 'jack';" to create an array; 5. Use Create an array using "$arr['name'] = '';".

The operating environment of this tutorial: windows10 system, php8.1.3 version, DELL G3 computer.

In PHP and other programming language programming, the creation of arrays is often used. In front-end development, js array creation can be directly created and assigned by [] and new Array(). But what are the ways to create arrays in PHP? After consulting the information and collecting and sorting it online, I summarized it:

1. Using array to create an array is the most common and convenient way:

$arr = array('a','b','c');
$arr[] = 'a' ; $arr[] = 'b' ; $arr[] = 'c';
$arr = array('name' => '关羽' , 'age' => 23 , 'sex' => '男')；

2. Sometimes you need to create a random array with a length of len, so you can use range():

Definition: array range(first, second, step) //first: the minimum value of the element second: the maximum value of the element step: the step size of the element (the amount to be increased)

$number = range(0,5);
print_r ($number);
   
//打印：Array ( [0] => 0 [1] => 1 [2] => 2 [3] => 3 [4] => 4 [5] => 5 )
   
$number = range(0,50,10);
print_r ($number);
   
//打印：Array ( [0] => 0 [1] => 10 [2] => 20 [3] => 30 [4] => 40 [5] => 50 )
   
$letter = range("a","d");
print_r ($letter);
   
//打印：Array ( [0] => a [1] => b [2] => c [3] => d )

3. Of course, under certain specific requirements , you need to store certain variables into an array, convert the variable names of these variables into key names, and convert the variable values ​​into key values ​​(premise: the variable exists):

$firstname = "Peter";
$lastname = "Griffin";
$age = "38";
$result = compact("firstname", "lastname", "age");
print_r($result);
   
//打印： Array ( [firstname] => Peter [lastname] => Griffin [age] => 38 )
   
$firstname = "Peter";
$lastname = "Griffin";
$age = "38";
$name = array("firstname", "lastname");
$result = compact($name, "location", "age");
print_r($result);
   
//打印：Array ( [firstname] => Peter [lastname] => Griffin [age] => 38 )
//由于$location变量不存在，所以存入不了数组

4. Two arrays are combined into a new array. The value of the first array is the key name of the new array, and the value in the second array is the key value of the new array: Definition: The array_combine() function can combine two arrays into A new array, one of which is the key name, and the other array's value is the key value.

$a1=array("a","b","c","d");
$a2=array("Cat","Dog","Horse","Cow");
print_r(array_combine($a1,$a2));
   
//打印：Array ( [a] => Cat [b] => Dog [c] => Horse [d] => Cow )

5. Create an array with a fixed length like the key value:

Definition: array_fill(start,number,value) //start: start Index number: The number of values ​​value: Array value

$a=array_fill(2,3,"Dog");
print_r($a);
   
//打印：Array ( [2] => Dog [3] => Dog [4] => Dog )

Create array format:

First format

$Array name = array('value', 'value', 'value',...);

This format does not specify the key of the elements in the array. PHP will automatically create the key in the form of a number, starting from 0. Accumulate in sequence.

Format of calling array: $array name[numeric key]

<?php
$arr = array(&#39;a&#39;,&#39;b&#39;,&#39;c&#39;); echo $arr[1]; //输出

2nd format

$array name[] = 'value ';

$array name[] = 'value';

$array name[] = 'value';

......

This kind The format also does not specify the keys of the elements in the array. PHP will automatically create the keys in the form of numbers, starting from 0 and accumulating sequentially.

Format of calling array: $array name[numeric key];

<?php
$arr[] = &#39;a&#39;; $arr[] = &#39;b&#39;; $arr[] = &#39;c&#39;; echo $arr[1]; //输出b

The third format

$array name = array(number Type key=> 'value', numeric type key=> 'value', numeric type key=> 'value',...);

Calling format: $array name[number Type of key];

<?php
$arr = array(1=>&#39;jack&#39;,2=>&#39;lucy&#39;,500=>&#39;hcoder&#39;); echo $arr[500]; //输出hcoder

This format uses integers as the keys of the array. PHP's support for arrays is very flexible, and you can arbitrarily define the numbers in the array.

If there are duplicate keys in the array, the last element will overwrite all previous keys, and the last one will be a valid value.

The 4th format

$Array name[integer type key] = 'value';

$Array name[integer type key] = 'value';

$array name[integer type key] = 'value';

......

Calling format: $array name[integer type key] ];

<?php
$arr[1] = &#39;jack&#39;; $arr[2] = &#39;lucy&#39;; $arr[500] = &#39;hcoder&#39;; echo $arr[500]; //输出hcoder

The 5th format (associative array)

$Array name=array('Key in string form'=>'Value',' Key in string form'=>'value',...);

Calling format: $array name['Key in string form'];

<?php
$arr = array(&#39;name&#39;=>&#39;张三&#39;, &#39;age&#39;=>18); echo $arr[&#39;age&#39;]; //输出18

th 6 formats (associative array)

$Array name['Key in string form']=>'Value';
$Array name['Key in string form'] =>'value';
......

Calling format: $array name['key in string form'];

<?php
$arr[&#39;name&#39;] = &#39;张三&#39;; $arr[&#39;age&#39;] = 18; echo $arr[&#39;age&#39;]; //输出18

In short, use $a[ ] and $a=array()

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