PHP array traversal foreach syntax structure and examples, foreach syntax
foreach()
PHP foreach() syntax structure is used to traverse operations or output arrays. foreach() can only be used to traverse arrays or objects. An error will occur when trying to use it for other data types or an uninitialized variable.
Grammar:
foreach (array as $value) statement // 或者: foreach (array as $key => $value) statement
In the above syntax, each loop assigns the value of the current unit to $value and moves the pointer inside the array forward one step. In the second syntax format, the key name of the current unit is also assigned to the variable $key in each loop.
Example:
<?php $arr_age = array("wang"=>18, "li"=>20, "zhang"=>25); foreach ($arr_age as $age) { echo $age,'<br />'; } ?>
Output of running this example:
18 20 25
Use array keys
<?php $arr_age = array("wang"=>18, "li"=>20, "zhang"=>25); foreach ($arr_age as $key=>$age) { echo $key,': ',$age,'<br />'; } ?>
Output of running the example:
wang: 18 li: 20 zhang: 25
When foreach starts executing, the pointer inside the array will automatically point to the first element, which means there is no need to call reset() before the foreach loop.
Foreach operates on a copy of the specified array, not the array itself. Modifications to the returned array elements will not affect the original array (see example below), but when the foreach loop runs to the end, the internal pointer of the original array will point to the end of the array.
<?php $arr_age = array("wang"=>18, "li"=>20, "zhang"=>25); foreach ($arr_age as $age) { $age = $age+10; echo $age,'<br />'; } // 输出原数组 print_r($arr_age); ?>
Output of running the example:
28 30 35 Array ( [wang] => 18 [li] => 20 [zhang] => 25 )
To modify the original array elements in foreach, you can do it by reference. Change the above example to:
<?php $arr_age = array("wang"=>18, "li"=>20, "zhang"=>25); foreach ($arr_age as &$age) { $age = $age+10; echo $age,'<br />'; } // 输出原数组 print_r($arr_age); ?>
Output of running the example:
18 20 25 Array ( [wang] => 28 [li] => 30 [zhang] => 35 )
Traverse multidimensional arrays
The foreach syntax structure can only be used to traverse one-dimensional arrays. To traverse multi-dimensional arrays, generally use foreach nested recursion or divide the original array into one-dimensional arrays and then perform foreach traversal.
Example of one- and two-dimensional array mixing:
<?php $arr_age = array("wang"=>18, "li"=>20, "zhang"=>array("name"=>"小张", "age"=>25)); foreach ($arr_age as $age) { if(is_array($age)){ foreach ( $age as $detail) { echo $detail,'<br />'; } } else { echo $age,'<br />'; } } ?>
The most appropriate processing method for traversing multi-dimensional arrays must be based on the actual data structure.
PHP arrays are implemented through HashTable tables, so foreach traverses the array according to the order in which elements are added. If you want to iterate by index size, you should use a for() loop.
for() loops through the array
If you are operating an array of continuous key values, you can also use a for() loop to traverse the array:
<?php $arr_age = array(18, 20, 25); $num = count($arr_age); for($i = 0; $i < $num; $i++){ echo $arr_age[$i]."<br />"; } ?>
You can also use list() and each() combined to traverse the array, but testing found that it is not as efficient as foreach().
The above PHP array traversal foreach syntax structure and examples are all the content shared by the editor. I hope it can give you a reference, and I hope you will support Bangkejia.

php把负数转为正整数的方法:1、使用abs()函数将负数转为正数,使用intval()函数对正数取整,转为正整数,语法“intval(abs($number))”;2、利用“~”位运算符将负数取反加一,语法“~$number + 1”。

实现方法:1、使用“sleep(延迟秒数)”语句,可延迟执行函数若干秒;2、使用“time_nanosleep(延迟秒数,延迟纳秒数)”语句,可延迟执行函数若干秒和纳秒;3、使用“time_sleep_until(time()+7)”语句。

php除以100保留两位小数的方法:1、利用“/”运算符进行除法运算,语法“数值 / 100”;2、使用“number_format(除法结果, 2)”或“sprintf("%.2f",除法结果)”语句进行四舍五入的处理值,并保留两位小数。

判断方法:1、使用“strtotime("年-月-日")”语句将给定的年月日转换为时间戳格式;2、用“date("z",时间戳)+1”语句计算指定时间戳是一年的第几天。date()返回的天数是从0开始计算的,因此真实天数需要在此基础上加1。

php判断有没有小数点的方法:1、使用“strpos(数字字符串,'.')”语法,如果返回小数点在字符串中第一次出现的位置,则有小数点;2、使用“strrpos(数字字符串,'.')”语句,如果返回小数点在字符串中最后一次出现的位置,则有。

方法:1、用“str_replace(" ","其他字符",$str)”语句,可将nbsp符替换为其他字符;2、用“preg_replace("/(\s|\ \;||\xc2\xa0)/","其他字符",$str)”语句。

在PHP中,可以利用implode()函数的第一个参数来设置没有分隔符,该函数的第一个参数用于规定数组元素之间放置的内容,默认是空字符串,也可将第一个参数设置为空,语法为“implode(数组)”或者“implode("",数组)”。

php字符串有下标。在PHP中,下标不仅可以应用于数组和对象,还可应用于字符串,利用字符串的下标和中括号“[]”可以访问指定索引位置的字符,并对该字符进行读写,语法“字符串名[下标值]”;字符串的下标值(索引值)只能是整数类型,起始值为0。


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