十一、数组

1、什么是数组？

数组是特殊的变量，它可以同时保存一个以上的值。数组能够在单一变量名中存储许多值，并且您能够通过引用下标号来访问某个值。

2、三种数组类型

索引数组 - 带有数字索引的数组
关联数组 - 带有指定键的数组
多维数组 - 包含一个或多个数组的数组

3、用array()创建数组

（1）、创建索引数组

<span class="hljs-variable">$its</span>=<span class="hljs-keyword">array</span>(<span class="hljs-string">"Google"</span>,<span class="hljs-string">"Apple"</span>,<span class="hljs-string">"Microsoft"</span>);print_r(<span class="hljs-variable">$its</span>);

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或

<span class="hljs-variable">$its</span>[<span class="hljs-number">0</span>]=<span class="hljs-string">"Google"</span>;<span class="hljs-variable">$its</span>[<span class="hljs-number">1</span>]=<span class="hljs-string">"Apple"</span>;<span class="hljs-variable">$its</span>[<span class="hljs-number">2</span>]=<span class="hljs-string">"Microsoft"</span>;print_r(<span class="hljs-variable">$its</span>);

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运行结果：Array ( [0] => Google [1] => Apple [2] => Microsoft )

（2）、创建关联数组

<span class="hljs-variable">$age</span>=<span class="hljs-keyword">array</span>(<span class="hljs-string">"Peter"</span>=><span class="hljs-string">"20"</span>,<span class="hljs-string">"Bill"</span>=><span class="hljs-string">"19"</span>,<span class="hljs-string">"Ken"</span>=><span class="hljs-string">"21"</span>);print_r(<span class="hljs-variable">$age</span>);

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或

<span class="hljs-variable">$age</span>[<span class="hljs-string">"Peter"</span>]=<span class="hljs-string">"20"</span>;<span class="hljs-variable">$age</span>[<span class="hljs-string">'Bill'</span>]=<span class="hljs-string">"19"</span>;<span class="hljs-variable">$age</span>[<span class="hljs-string">"Ken"</span>]=<span class="hljs-string">"21"</span>;print_r(<span class="hljs-variable">$age</span>);

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运行结果：Array ( [Peter] => 20 [Bill] => 19 [Ken] => 21 )

4、用count()获取数组长度

<span class="hljs-variable">$its</span>=<span class="hljs-keyword">array</span>(<span class="hljs-string">"Google"</span>,<span class="hljs-string">"Apple"</span>,<span class="hljs-string">"Microsoft"</span>);<span class="hljs-variable">$age</span>=<span class="hljs-keyword">array</span>(<span class="hljs-string">"Peter"</span>=><span class="hljs-string">"20"</span>,<span class="hljs-string">"Bill"</span>=><span class="hljs-string">"19"</span>,<span class="hljs-string">"Ken"</span>=><span class="hljs-string">"21"</span>);<span class="hljs-keyword">echo</span> count(<span class="hljs-variable">$its</span>).<span class="hljs-string">"<br />"</span>;<span class="hljs-keyword">echo</span> count(<span class="hljs-variable">$age</span>);

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运行结果：
3 3

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5、用for和foreach遍历数组

（1）、用for遍历索引数组

<span class="hljs-variable">$its</span>=<span class="hljs-keyword">array</span>(<span class="hljs-string">"Google"</span>,<span class="hljs-string">"Apple"</span>,<span class="hljs-string">"Microsoft"</span>);<span class="hljs-keyword">for</span>(<span class="hljs-variable">$i</span>=<span class="hljs-number">0</span>;<span class="hljs-variable">$i</span><count(<span class="hljs-variable">$its</span>);<span class="hljs-variable">$i</span>++){    <span class="hljs-keyword">echo</span> <span class="hljs-variable">$its</span>[<span class="hljs-variable">$i</span>].<span class="hljs-string">"<br />"</span>;}

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运行结果：
Google Apple Microsoft

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（2）、用foreach遍历关联数组

<span class="hljs-variable">$age</span>=<span class="hljs-keyword">array</span>(<span class="hljs-string">"Peter"</span>=><span class="hljs-string">"20"</span>,<span class="hljs-string">"Bill"</span>=><span class="hljs-string">"19"</span>,<span class="hljs-string">"Ken"</span>=><span class="hljs-string">"21"</span>);<span class="hljs-keyword">foreach</span>(<span class="hljs-variable">$age</span> <span class="hljs-keyword">as</span> <span class="hljs-variable">$value</span>){<span class="hljs-keyword">echo</span> <span class="hljs-variable">$value</span>.<span class="hljs-string">"<>"</span>;}

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运行结果：
20 19 21

6、数组排序

sort() - 以升序对数组排序
rsort() - 以降序对数组排序
asort() - 根据值，以升序对关联数组进行排序
ksort() - 根据键，以升序对关联数组进行排序
arsort() - 根据值，以降序对关联数组进行排序
krsort() - 根据键，以降序对关联数组进行排序

如何记住它们？

r—-reduce，减少
a—-value，值（不知道是不是，暂且这样记）
k—-key，键

<span class="hljs-variable">$age</span>=<span class="hljs-keyword">array</span>(<span class="hljs-string">"Peter"</span>=><span class="hljs-string">"20"</span>,<span class="hljs-string">"Bill"</span>=><span class="hljs-string">"19"</span>,<span class="hljs-string">"Ken"</span>=><span class="hljs-string">"21"</span>);<span class="hljs-keyword">foreach</span>(<span class="hljs-variable">$age</span> <span class="hljs-keyword">as</span> <span class="hljs-variable">$value</span>){<span class="hljs-keyword">echo</span> <span class="hljs-variable">$value</span>.<span class="hljs-string">"<br />"</span>;}arsort(<span class="hljs-variable">$age</span>);<span class="hljs-keyword">foreach</span>(<span class="hljs-variable">$age</span> <span class="hljs-keyword">as</span> <span class="hljs-variable">$value</span>){<span class="hljs-keyword">echo</span> <span class="hljs-variable">$value</span>.<span class="hljs-string">"<br />"</span>;}

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运行结果：
20 19 21 21 20 19