php数组

php中数组分为：索引数组和关联数组；

　　索引数组：数组的索引值是整数，以0开始，通过位置来标识的时候使用索引数，下标从0开始；

　　关联数组：以字符串作为索引，关联数组更像操作表，索引值为列名，用于访问列的数据

　　key-value

数组的定义：（两种）

<?php
    //数组的定义
    /*
    $arr1[0] = "PHP";
    $arr1[1] = "MySQL";
    $arr1[2] = "Apache";
    $arr1[3] = "Linux";
   
    $arr1[] = "PHP";
    $arr1[] = "MySQL";
    $arr1[] = "Apache";
    $arr1[] = "Linux";
    */
    
    //关联数组的直接定义
    $arr1["brand"] = "iphone5";
    $arr1["os"] = "ios";
    $arr1["price"] = 4980;
    //打印数组，print_r
    print_r($arr1);

?>

<?php
    //使用array语句来定义数组
    $arr1 = array("PHP","MySQL","Apache","Linux");
    
    $arr2 = array(
        "brand" => "Lumia 900",
        "os" => "wp8",
        "price" => 4700
    );
    echo "<pre>";
    print_r($arr2);
    echo "</pre>";    
?>

数组的遍历：

数组的遍历分为三种，for、foreach、while+list+each

for有局限性，只能遍历关联数组；

<?php
    // 数组的遍历
    $arr1 = array(2,3,4,5,6,7);
    $arr2 =  array(
        "brand" => "Lumia 900",
        "os" => "wp8",
        "price" => 4700
    );
    //不推荐$i < count($arr1)
    $len = count($arr2);

    for($i = 0; $i < $len; $i++){
        echo $arr2[$i]."<br />";
    }
?>

foreach几乎专门为数组量身定制

1、foreach($arr as $val)

{echo $val.'<br/>';}

2、foreach($arr as $key =>$value)

{echo $key.='='.$value.'<br/>';}

<?php
    //foreach 的用法
    $arr2 =  array(
        "brand" => "Lumia 900",
        "os" => "wp8",
        "price" => 4700
    );
   
    $arr1 = array("PHP","MySQL","Apache","Linux");
   
    foreach($arr1 as $key => $val){
        echo $key."=".$val."<br />";
    }
?>

<?php
    //while+ list + each
    $arr1 = array(
        "brand" => "Lumia 900",
        "os" => "wp8",
        "price" => 4700
    );
    echo "<pre>";
    print_r(each($arr1));
    echo "</pre>";

    list($k,$v) = each($arr1);
    echo $k."<br />";
    echo $v."<br />";
    /*
    while(list($k,$v) = each($arr1)){
        echo $k ."=".$v."<br />";
    */
    }    
?>

while+list+each：使用起来比较麻烦，不建议；list是种结构，只针对索引有效，仅能用于数字索引的数组并假定数字索引从0开始

除非数组是被引用，foreach所操作的是指定数组的一个拷贝，而不是该数组本身，在php里数组是通过值传递，对象是引用传值；