php数组总结篇(一）

　　数组
1.数组的下标是整型数值或者是字符串类型。
eg1．索引数组的键是______，关联数组的键是______。
2.字符串作为索引的时候，应加上引号。常量或者变量不用加引号，否则无法编译。
在php中，没有引号的字符串会自动生成一个裸字符串，而 PHP 可能会在以后定义此常量，不幸的是你的代码中有同样的名字，那么这个字符串就被重新赋值。
eg2.<?php
// 显示所有错误
error_reporting(E_ALL);
$arr = array(fruit => apple, veggie => carrot);
// 正确
print $arr[fruit]; // apple
print $arr[veggie]; // carrot
// 不正确。This works but also throws a PHP error of
// level E_NOTICE because of an undefined constant named fruit
//
// Notice: Use of undefined constant fruit - assumed fruit in...
print $arr[fruit]; // apple
// Lets define a constant to demonstrate whats going on. We
// will assign value veggie to a constant named fruit.
define(fruit,veggie);
// Notice the difference now
print $arr[fruit]; // apple
print $arr[fruit]; // carrot
// The following is okay as its inside a string. Constants are not
// looked for within strings so no E_NOTICE error here
print Hello $arr[fruit]; // Hello apple
// With one exception, braces surrounding arrays within strings
// allows constants to be looked for
print Hello {$arr[fruit]}; // Hello carrot
print Hello {$arr[fruit]}; // Hello apple
// This will not work, results in a parse error such as:
// Parse error: parse error, expecting T_STRING or T_VARIABLE or T_NUM_STRING
// This of course applies to using autoglobals in strings as well
print Hello $arr[fruit];
print Hello $_GET[foo];
// Concatenation is another option
print Hello . $arr[fruit]; // Hello apple
?>
3.键值问题
$a[color] = red;
$a[taste] = sweet;
$a[shape] = round;
$a[name] = apple;
$a[] = 4; // key will be 0
$b[] = a; // key will be 0
$b[] = b; // key will be 1
$b[] = c; // key will be 2
switching = array( 10, // key = 0
5 => 6,
3 => 7,
a => 4,
11, // key = 6 (maximum of integer-indices was 5)
8 => 2, // key = 8 (integer!)
02 => 77, // key = 02
0 => 12 // the value 10 will be overwritten by 12
);
<?php
$multi_array = array(red,
green,
42 => blue,yellow => array(apple,9 => pear,banana,orange => array(dog,cat,iguana)));
?>
A．$multi_array[yellow][apple][0]
B．$multi_array[blue][0][orange][1]
C．$multi_array[3][3][2]
D．$multi_array[yellow][orange][cat]
E．$multi_array[yellow][orange][1]
--------------------------------待续待续待续------
4.array_walk
5.var_dump
6.array_intersect
7.array_sum
8.array_count_values
9.array_flip
10.natsort
11.ksort(),asort(),krsort(),sort(),usort()
12.array_reverse()
13.array_merge
14.reset
-------------------------------待续待续待续------
15.array_combine
16array_count_values
17.array_diff
18.array_filter
19.array_search