Introduction to PHP Arrays_PHP Tutorial

Introduction to PHP arrays

Array basics:

In php, the subscript of an array can be an integer or a string

In php, the order of the elements of the array is not determined by the subscript, but by the order of their "joining"

Definition:

$arr1 = array(element 1, element 2,...);

array(1,1.1,5,'abc',true,false); //Any data can be stored, at this time it is the default subscript

array(2=>1,4=>1.1,3=>5,7=>'abc',0=>true); //The subscripts can be set arbitrarily (no order required, No need to be consecutive)

array(2=>1,1.1,1=>5,'abc',0=>true); //You can add a subscript or not. If you don't add a subscript, it will be the default subscript. Mark

                                                                                                                                                                            to

// The number of this number is: 2, 3, 1, 4, 0

array(2=>1,'dd'=>5,1=>1.1,'abc',0=>true); //Mixed subscripts, also follow the default subscript rules

array(-2=>1,'dd'=>5,1.1,'abc',true); //Negative subscripts are not included in the integer subscripts, but are only treated as character subscripts

// The last three sets of this array are: 0,1,2

array(2.7=>1,'dd'=>5,1=>1.1,'abc',true); //The floating point number subscript will be automatically converted to an integer, and the decimal part will be removed directly

array("2.7"=>1,'dd'=>5,"11"=>1.1,'abc',true); //Pure numeric string subscript, treated as a number

array(2=>1,'dd'=>5,true=>1.1,'abc',false=>true); //Boolean value is used as subscript, then true is 1, false is 0

array(2=>1,'dd'=>5,2=>1.1,'abc',true); //If the subscript is repeated with the previous one, it will simply overwrite the value of the previous subscript with the same name.

Other forms:

$arr1[] = 1;

$arr1[] = 5;

$arr1[] = 1.1;

       … //Use [] directly after the variable to become an array, and assign values ​​​​in sequence

$arr2['aa'] = 1;

$arr2['bb'] = 5;

$arr2[5] = 1.1;

     …                                                                                                                                                    //The subscript written in this form is actually almost the same as using the array syntax structure

Classification of arrays:

From the key-value relationship, it is divided into:

Associative array: usually refers to an array whose subscript is a string, and the string can roughly express the meaning of the data

              Example: $person = array("name" => "poe", "age" => 18, "edu" => "University graduate");

Index array: usually refers to an array whose subscript strictly starts from 0 and is a continuous numeric subscript - similar to js array

Divided from the array level:

One-dimensional array: Each element value in an array is an ordinary value (non-array value)

Example: $ Person = Array ("name" = & gt; "poe", "age" = & gt; 18, "edu" = & gt; "college graduation");

Two-dimensional array: Each item in an array is also a one-dimensional array.

$person = array(

                                             "name" => array("xiaohua","xiaofang),

                                                                                                                                                                                                                  "age" => array(18,22),

"Edu" = & GT; Array ("University Graduation", "Primary School",)

                      );

Multi-dimensional array: and so on. . .

The general syntax form of multi-dimensional arrays:

$ v1 = number of array names [Nubble] [Laying] [......]

Array traversal:

Basic syntax for traversal:

foreach($arr as [$key =>] $value) {

                //Here you can perform all possible operations on $key and $value -- because they are just a variable

//$key represents the subscript of each element obtained, which may be a number or a string

//$value represents the value of the element obtained each time, which may be of various types

                             //This loop structure will traverse from the first item of the array to the last item, and then end

}

Array pointers and traversal principles:

Each array has a "pointer" inside it, which determines the element obtained when the array currently takes value

During the foreach traversal process, it all relies on this pointer.

Example: $arr1 = array(2=>1,'dd'=>5,1=>1.1,'abc',0=>true);

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In addition to the position setting of the foreach loop, pointers also have some other functions that rely on pointers:

1: $v1 = current($arr1); //Get the value of the element pointed to by the current pointer in $arr1. If there is no element pointed to, it is false

2: $v1 = key($arr1); //Get the subscript of the element pointed to by the current pointer in $arr1. . . . . . . . . . . . .

3: $v1 = next($arr1); //Move the pointer to the "next element", and then get the value of the next element

4: $v1 = prev($arr1); //Move the pointer to the "previous element", and then get the value of the previous element

5: $v1 = reset($arr1); //Move the pointer to the "first element" and get the value of the element

6: $v1 = end($arr1); //Move the pointer to the "last element" and get the value of the element

7: $v1 = each($arr1); //Get the subscript and value of the current element, and then move the pointer to the next position

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