Definition and filling of PHP learning Arrays

PHP array. To put it bluntly, each array of associated data is saved in the form of [index, value. The index starts with 0 by default. If no index is specified, PHP automatically generates an index from 0. If an index is specified, PHP starts with the next integer of the maximum positive integer of the index. If you specify decimal places, PHP will take the integer part as the index.

In addition, let's talk about other small items in the array:
Array () can declare an empty array;
Array [] = $ value: When an array exists, an array is generated and data is appended when the array is not saved.
Array [$ index] = $ value when an array exists, an array is generated and data is appended when the array does not exist.

See the following code:
Copy codeThe Code is as follows:
// Declare an array
$ Test01 = array ();
// Append data
$ Test01 [] = "a"; // array (0 => "");
// Append the data whose index is "a" and whose data is "B"
$ Test01 ["a"] = "B"; // array (0 => "a", "a" => "B ");
// Modify the data whose index is 0
$ Test01 [0] = "c"; // array (0 => "c", "a" => "B ");
// Another declaration method
$ Test02 = array ("a", "B", "c"); // array (0 => "a", 1 => "B ", 2 => "c ");
// Although the data of a string index is declared, the default index starts from 0.
$ Test03 = array ("a" => "a", "B", "c"); // array ("a" => "", 0 => "B", 1 => "c ");
// The maximum index in the Declaration is 2. Although the index is 0 recently, the default index starts from 3.
$ Test04 = array (2 => "a", 0 => "B", "c"); // array (2 => "", 0 => "B", 3 => "c ");
// Declaring a decimal index takes the integer part of the index. If an index is specified, the previously declared value is modified.
$ Test05 = array ("a", 2.7 => "B", 0 => "c"); // array (0 => "c ", 2 => "B ");
// Although a negative index is declared, the default index starts from 0.
$ Test06 = array (-2 => "a", "B", "c"); // array (-2 => "", 1 => "B", 2 => "c ");
// Multi-dimensional array Definition
$ Test07 = array ($ test01, $ test02, $ test03 );

Then we will introduce some filling functions of the array. Most of these functions can be found in the manual, so we will just give a brief introduction.
Range ($ n, $ m); specifies the range of values. For example, range (2, 4) generates an array (2, 3, 4 ).
Count ($ array); returns the size of the array.
Array_pad ($ array, $ length, $ value); returns an array with a length of $ length. The complement value of the original array is $ value, and the length is sufficient to return the original array.