What is a variable
Description: A way to store data in php is the amount that i can change. This way It is to open up a space in the memory that can store data, give this space a name, and the space at this time can be called a variable. This value can be changed during operation (recommended learning: PHP video tutorial)
The name of the current space is the variable name, and the data of the current space (eight kinds of data Type) is called the variable value
Define the variable and assign the value
Define the variable: $variable name; Note that variables defined in this way are OK, but not Use, direct output will report an error, it must be followed by a variable value before you can use
to define variables and assign values: $variable name = variable value;
<?php $a; echo $a; $a =1; echo $a; ?>
Rules for defining variables
Variable names are case-sensitive
It is recommended to use meaningful names for variable names. When you see the variable name, you will know what it means, such as $name, Naming rules for $age, $sex, $get_user_name: must be composed of numbers, letters, and underscores and cannot start with a number. For example: $a1, $A1, $a_1, $_a1, $_2 are all acceptable but cannot be $1a.
Eight data types of variables
Scalar types: int (integer type), float (floating point type), boolean (Boolean type), string (String type)
Composite type: array (array), object (object)
Special type: null (empty), resource (resource)
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php把负数转为正整数的方法:1、使用abs()函数将负数转为正数,使用intval()函数对正数取整,转为正整数,语法“intval(abs($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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