PHP数组练习及答案

1.一维数组是最简单的数组，其定义形式是？

$arr = array()或者$arr = [];

2.怎么判断一个变量是否为空，怎么判断一个变量是否存在？

empty($str); isset($str);

3.如何获取数组$arr = array(array(‘a’,’b’,’c’));中的值’c’ ?

$arr[0][2];

4.如何定义一个三维数组？

$arr = array(array(array()));或者$arr = [[[]]];

5.怎么才能从数组$multi_array中找出值cat？

$multi_array = array(

"red","green",

42 => "blue",

"yellow" => array("apple",9 => "pear","banana", "orange" => array("dog","cat","iguana")) );

$multi_array*‘yellow’+*‘orange’+*1+;

6.下面数组$arr中，打印$arr[1][1]输出的值是什么？

$arr = array(

array('jack','boy',23,'18nan'=>array(18000,180,18)),

array('rose','girl',18)

);

答案：girl

7.遍历输出数组$arr = array(1=>’ff’,‘aa,’dd,’cc’,’eee’);

foreach($arr as $value){

echo $value;

}

8.求数组$arr = array(‘qwer,’jkls’,’cc’,’eee’)中元素的个数。答案：count($arr);

9.运行下面代码输出的内容是？

$arr=array(5=>1,12=>2);

$arr[]=3;

$arr["x"]=4;

print_r($arr); echo "
";

unset($arr[5]);

print_r($arr); echo "
";

unset($arr);

print_r($arr);

Array( [5] => 1 [12] => 2 [13] => 3 [x] => 4 )

_____________________________________________ Array([12] => 2 [13] => 3 [x] => 4)

______________________________________________

10.如何取出字符串$str = “abcdefg”;中的值‘f’？

答案：$str[5];