In php, arrays can store values of any PHP type. If no key name is specified for the given value, the current largest integer index value will be taken, and the new key name will be the value plus one, which is PHP array
has three array types:
numeric array
Array with numeric ID keys
Associative array
Each ID key in the array is associated with a value
Multidimensional array
Array containing one or more arrays
An array in PHP is actually an ordered map. A map is a type that associates values to keys. This type is optimized in many ways, so it can be treated as a real array, or list (vector), hash table (which is an implementation of map), dictionary, set, stack, queue and many more possibilities. The value of an array element can also be another array. Tree structures and multidimensional arrays are also allowed.
You can use the array() language structure to create a new array. It accepts any number of comma-separated key => value pairs.
key can be integer or string. If key is the standard representation of an integer, it is interpreted as an integer (e.g. "8" will be interpreted as 8, and "08" will be interpreted as "08"). Floating point numbers in key are rounded to integers. In PHP, indexed arrays are the same as associative arrays, they can contain both integer and string subscripts.
The value can be any PHP type.
If no key is specified for the given value, the current largest integer index value is taken, and the new key name will be that value plus one. If the specified key name already has a value, the value will be overwritten.
Using TRUE as the key name will make integer 1 the key name. Using FALSE as the key name will make integer 0 the key name. Using NULL as a key name is equivalent to using an empty string. Using an empty string as a key will create (or overwrite) a value with an empty string as the key, which is different from using empty square brackets.
Arrays and objects cannot be used as keys. Doing so will result in a warning: Illegal offset type.
Create/modify using square bracket syntax
If $arr does not exist yet, a new one will be created. This is also an alternative way to define an array. To change a value, just assign it a new value. If you want to delete a key/value pair, use unset() on it.
Note: If square brackets are given but no key name is specified, the current maximum integer index value is taken, and the new key name will be that value + 1. If there is no integer index currently, the key name will be 0. If the specified key name already has a value, the value will be overwritten.
Note that the maximum integer key name used here is not necessarily currently in the array. It just needs to have existed since the last time the array was reindexed.
Array indexes expressed as strings should always be quoted. For example, use $foo['bar'] instead of $foo[bar]. But why is $foo[bar] wrong?
The reason is that this code has an undefined constant (bar) instead of a string ('bar' - note the quotes), and PHP may define this constant later, unfortunately your code has the same name. It works because PHP automatically converts a bare string (a string without quotes and not corresponding to any known symbol) into a normal string whose value is that bare string. For example, if there is no constant defined as bar, PHP will replace it with 'bar' and use that.
Example 1
In this example, the ID key is automatically assigned:
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Example 2 In this example, we manually assigned the ID key:
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$names[0] = "Peter"; $names[1] = "Quagmire"; $names[2] = "Joe"; |
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$names[0] = "Peter"; $names[1] = "Quagmire"; $names[2] = "Joe"; |
You can use these ID keys in scripts:
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$names[0] = "Peter"; echo $names[1] . " and " . $names[2] . " are ". $names[0] . "'s neighbors";
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Example 1

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。

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。

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。

在php中,可以使用substr()函数来读取字符串后几个字符,只需要将该函数的第二个参数设置为负值,第三个参数省略即可;语法为“substr(字符串,-n)”,表示读取从字符串结尾处向前数第n个字符开始,直到字符串结尾的全部字符。


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