PHP数组和数据结构（上）

1.数组的声明

两种方法：

• 直接给数组元素赋值
• 使用array（）函数声明

说明：

（1）索引数组的下标可以是非连续的值，只要在初始化时指定非连续的下标值即可

• 如果指定的下标值已经声明过，则属于对变量重新赋值。
• 如果没有指定索引值的元素与指定索引值的元素混在一起赋值时，没有指定索引值的元素默认索引值，将紧跟指定索引值元素中最高的索引值递增。

代码示例：

<?php
$a[]=1;
$a[10]="高某";
$a[]="A公司";   // 此时A公司的下标成为11
$a[]="北京市";   //北京市的下标为12
$a[]="(010)987654321"; //下标是13
$a[10]="gao@qq.com";//下标是11，下标11的值改为gao@qq.com
$a[]="IT"; //IT的下标值为14
var_dump($a);
?>

运行结果：

（2）使用array（）函数声明

使用array（）语言构造来新建一个数组，它接受一定数量用逗号分隔的key => value参数对

代码示例：

<?php
//如果不使用 => 符号指定下标，默认为索引数组。默认的索引值也是从0开始一次增加
$a=array(1,"高某","A公司","北京市","(010)987654321","gao@qq.com");
//使用 => 可以指定非连续的索引值
$a1=array(1,10=>"高某","A公司","北京市",10=>"(010)987654321","gao@qq.com");
var_dump($a);
echo "<br/>";
var_dump($a1);
?>

运行结果：

2.数组元素的访问

代码示例：

<?php
$a=array(1,"高某","A公司","北京市","(010)987654321","gao@qq.com");
//使用 => 可以指定非连续的索引值
$a1=array('xiaoming'=> "IT",'xiaohei'=>"english",'xiaolan'=>"chinese");
//直接指定元素下标
echo $a[1];
echo "<br/>";
//指定键：
echo $a1['xiaohei'];
?>

运行结果：

3.二维数组

（1）数字索引方式

$a=array(array(1,"高某","A公司","北京市","(010)987654321","gao@qq.com"),
        array(2,"李某","B公司","上海市","(010)987654323","li@qq.com"),
        array(3,"杨某","C公司","济南市","(010)987654324","yang@qq.com"),
        array(4,"孙某","D公司","威海市","(010)987654325","sun@qq.com")
);

（2）使用array（）函数

$a2=array("北京联系人"=>array(1,"高某","A公司","北京市","(010)987654321","gao@qq.com"),
          "上海联系人"=>array(2,"李某","B公司","上海市","(010)987654323","li@qq.com"),
          "济南联系人"=>array(3,"杨某","C公司","济南市","(010)987654324","yang@qq.com")
);

（3）二维数组的访问

<?php
$a=array(array(1,"高某","A公司","北京市","(010)987654321","gao@qq.com"),
        array(2,"李某","B公司","上海市","(010)987654323","li@qq.com"),
        array(3,"杨某","C公司","济南市","(010)987654324","yang@qq.com"),
        array(4,"孙某","D公司","威海市","(010)987654325","sun@qq.com")
);
echo $a[1][1];
echo "<br/>";
$a2=array("北京联系人"=>array(1,"高某","A公司","北京市","(010)987654321","gao@qq.com"),
          "上海联系人"=>array(2,"李某","B公司","上海市","(010)987654323","li@qq.com"),
          "济南联系人"=>array(3,"杨某","C公司","济南市","(010)987654324","yang@qq.com")
);
echo $a2["上海联系人"][1];
?>

4 .数组的遍历

(1)for循环遍历

<?php
$a=array(array(1,"高某","A公司","北京市","(010)987654321","gao@qq.com"),
        array(2,"李某","B公司","上海市","(010)987654323","li@qq.com"),
        array(3,"杨某","C公司","济南市","(010)987654324","yang@qq.com"),
        array(4,"孙某","D公司","威海市","(010)987654325","sun@qq.com")
);
//count是得到一维长度
echo count($a)."<br/>";
for($i=0;$i<count($a);$i++){
    for ($j=0;$j<count($a[$i]);$j++){
        echo $a[$i][$j];
    }
    echo "<br/>";
}
?>

运行结果：

（2）foreach遍历

<?php
$a[]=1;
$a[10]="高某";
$a[]="A公司";   // 此时A公司的下标成为11
$a[]="北京市";   //北京市的下标为12
$a[]="(010)987654321"; //下标是13
$a[10]="gao@qq.com";//下标是11，下标11的值改为gao@qq.com
$a[]="IT"; //IT的下标值为14
foreach ($a as $value){
    echo $value."<br>";
}
?>

运行结果：

<?php
$a=array(
        "ID"=>"1",
        "name"=>"xiaohua",
        "city"=>"shanghai",
        "job"=>"IT"
 
);
foreach ($a as $key=>$value){
    echo "<dd>$key:$value<dd>";
}
?>

运行结果：