Arrays (1)

First, the way the array is defined:

An array is a way to store data that can store multiple values, each of which is distinguished by a different key.

Number on box with key

Value-Box Contents

　　

1 $arr Array (' name ' = ' Wangwu ', ' age ' = ');//define an array 2 Print_r ($arr); 3 Echo ' <br/> '; 4 Echo $arr [' Name '];//the value of the Access array key to name

Ii. Types of arrays

Classification of arrays: indexed arrays; associative arrays; two-dimensional arrays; multidimensional arrays

1, indexed array--the key does not have to have special meaning, the pure number from 0 increments the array, this is called "the Index array".

　　　　

1 $arr Array (0=> ' A ',1=> ' B ',2=> ' C ',3=> ' d '); 2 Print_r ($arr);

2. Associative arrays

The string does the key, generally can reflect the content of the unit.

1 $arr = array (' name ' = ' Wangwu ', ' age ' + ', ' hobby ' = ' basketball ');//associative array 2 print_r ($arr); 

3, two-dimensional arrays, multidimensional arrays

$arr 2 = Array (' name ' = ' Lisi ', ' age ' =>25, ' hobby ' =>array (' Football ', ' Pingpang '));

Third, array key rules

1, the key can not be assigned, the system will 0,1,2 、、、 increment allocation

$arr = Array (' A ', ' B ', ' C ');

Print_r ($arr);

2, if there are key assignments, and some do not assign, will be from the previous key, take the largest key to start incrementing

　　　　

1 $arr 1 Array (' name ' = ' Lisi ', ' age ' = ' ', ' running '); 2 Print_r ($arr 1);

Operation Result:

Array ([name] = Lisi [age] = [0] = running)

　　

1 $arr 2 Array (0=> ' A ',1=> ' B ', ' C ',5=> ' d ', ' e ', ' f '); 2 Print_r ($arr 2);

Operation Result:

Array ([0] = a [1] = b [2] = = c [5] + d [6] = e [7] = f)

1 $arr 2 Array (0=> ' A ',1=> ' B ', ' C ',5=> ' d ', ' e ', ' f '); 2 Print_r ($arr 2);

Operation Result:

Array ([0] = a [1] = b [2] = = c [5] + d [6] = e [7] = f)

3. What if the key assignment repeats

Its keys are not repeatable for an array

If the key is repeated, the following key with the same name overrides the previous

　　

1 $arr 3 Array (' A ', ' B ', ' C ',2=> ' d ',2=> ' e '); 2 Print_r ($arr 3);

Array ([0] = a [1] = b [2] = = e)

Attention:

There are only two types of keys for an array, integer and string

Keys are floating-point, string-type integers, and null

Key for floating-point and down-rounding

If the string is exactly understood as an integer, it is also converted to an integer

Null is understood by an empty string

　　　　

1 $arr Array (2=> ' This ',2.5=> ' Day ',2.5=> ' is ', ' 2 ' = ' week ',null= ' end '); 2 3 Print_r ($arr);

Operating effect:

Array ([2] = = Week [] = end)

In the actual development:

Do not encounter these more troublesome arrays

Typically associative arrays and automatically generated indexed arrays

Iv. manipulating arrays of elements

The array is a composite data, which puts a lot of data print_r () will print out all the data in the array of specific units to operate arrays of elements, delete, change, check

1. Remove the value of a unit by itself and use the key to fetch the $ array name [key]

　　

1 $arr Array (' A ', ' B ', ' C '); 2 Echo $arr [1];

Operation Result:

B

2. Take out the values of the two-dimensional array

The array hierarchy is at most 3 levels, otherwise it cannot be intuitively understood.

　　　　

1 $arr 2 Array (' name ' = ' Lisi ', ' age ' =>23, ' hobby ' = =array(' Basketball ', ' Football ', ' Pingpang ')); 2 Echo $arr 2 [' Hobby '] [0];

Basketball

3. Change the value of an array cell

　　

1 $arr 2 Array (' name ' = ' Lisi ', ' age ' =>23, ' hobby ' = =array(' Basketball ', ' Football ', ' Pingpang ')); 2 $arr 2 [' Hobby '] [0] = ' swiming '; 3 Print_r ($arr 2);

Operation Result:

Array ([name] = Lisi [age] = [hobby] = = Array ([0] = swiming [1] = = Football [2] = = Pingpang))

4. Add an array unit

　　

1 $arr 2 Array (' name ' = ' Lisi ', ' age ' =>23, ' hobby ' = =array(' Basketball ', ' Football ', ' Pingpang ')); 2 $arr 2 [' area '] = ' Beijing '; 3 Print_r ($arr 2);

Operation Result:

Array ([name] = Lisi [age] = [hobby] = = Array ([0] = basketball [1] = = Football [2] = = Pingpang ) [Area] = Beijing)

5. Delete array cells

　　

1 $arr 2 Array (' name ' = ' Lisi ', ' age ' =>23, ' hobby ' = =array(' Basketball ', ' Football ', ' Pingpang ')); 2 unset ($arr 2[' Hobby ']); 3 Print_r ($arr 2);

Operation Result:

Array ([name] = Lisi [age] = 23)

V. Iterating through an array

1. Remove each cell of the array

　　

1 $arr Array (' A ', ' B ', ' C ', ' d '); 2 Echo $arr [0]. ' <br/> '; 3 Echo $arr [1]. ' <br/> '; 4 Echo $arr [2]. ' <br/> '; 5 Echo $arr [3]. ' <br/> ';

Operation Result:

A
B
C
D

1 $arr Array (' A ', ' B ', ' C ', ' d '); 2  for ($i= 0; $i<count($arr); $i+ +) {3     echo$arr{$i}, ' <br/> '  ; 4 }

2. How do associative arrays take out each array cell?

Its key is a string, there is no rule, foreach is specifically used to loop the array,

Very fast, the variable name ($k, $v) of the key value inside the foreach is any valid variable name

　　

1 $arr Array (' name ' = ' Zhangsan ', ' age ' =>24, ' area ' = ' Beijing '); 2 foreach ($arras$k= +$v) {3     Echo $k, ': ',$v, ' <br/> '; 4 }

Name:zhangsan
Age:24
Area:beijing

3. Cyclic value only

　　

1 $arr Array (' name ' = ' Zhangsan ', ' age ' =>24, ' area ' = ' Beijing '); 2 foreach ($arras$v) {3     Echo $v, ' <br/> '; 4 }

Operation Result:

Zhangsan
24
Beijing

4.array_keys-returns all the key names in the array foreach has no way to single loop out the health

　　

1 $arr Array (' name ' = ' Zhangsan ', ' age ' =>24, ' area ' = ' Beijing '); 2 3 Print_r (array_keys($arr));

Operation Result:

Array ([0] + = name [1] = age [2] = area)

5. Change the value of each cell of the array below to twice times the original

　　

1 $stu Array (' San ' =>3, ' Lisi ' =>4, ' Wang ' =>5, ' Zhao ' =>5); 2 foreach ($stuas$k= +$v) {3     $stu [$k$v* *; 4 }5print_r($stu);

Array ([san] = 6 [Lisi] + 8 [Wang] = [Zhao] 10)

Array (1)