In the article "Talk about HTML syntax", I have introduced basic HTML syntax. It is possible to compile a static Web page, but it is very important to dynamically interact information. For example, the membership system of some websites requires the operation of back-end programs for member registration and login. The CGI programs used by many websites are mainly written in Perl, ASP, Java, and PHP, and what we are going to use is PHP. It's completely free, thanks to those obscure programmers. The structure of PHP is similar to the C language, which is in compliance with the "learn in one place, program anywhere" mentioned in the C language. I believe that people who have learned the C language can easily get started with PHP. Let’s introduce some PHP syntax first. This article is suitable for beginners to learn.
There are also some differences between PHP and C language, or it may be more flexible than C language to some extent. In C language, variables must be defined before they can be used. In PHP, variables do not need to be defined in advance and can be used directly. The type of the variable is automatically generated when assigning a value. The types of PHP variables are divided into: integer (int), double (double), string (string), array (array), and object (object).
When the integer size exceeds its range, it is automatically converted to double precision. The value range is as follows:
┌─────┬─────┬──────┬──── ────────┐
│ Declaration type │ Length (bits) │ Length (bytes) │ Value range │
├─────┼─────┼─── ───┼────────────┤
│ int │ 32 │ 4 │-2147483647~2147483647 │
├─────┼─────┼── ────┼────────────┤
│ double │ 32 │ 4 │ 1.7E-308~1.7E+308 │
└─────┴── ───┴──────┴────────────┘
String, usually represented by "" (double quotes). It can also be expressed with (single quotes), as follows:
$a="abc";
$b="abc$a";
$c=abc$a;
$d="" cde"";
$e="cde";
Various variables in PHP are distinguished by adding "$" before the variable name.
Note that the content of $b is abcabc, the content of $c is abc$a, the content of $d is "cde", and the content of $e is also "cde". It can be seen that the variable names in the content in double quotes will be replaced, but those in single quotes will not. The content in double quotation marks needs to be escaped, such as $, which should be represented by $, but the content in single quotation marks should not be escaped.
The array syntax in PHP is:
Array name [index]
The index can be a number or a text. But it is not recommended to use text because it does not make much sense. It is also more flexible than other languages for arrays. For example:
$names[]=100;
$names[]=200;
$names[]="hi,how are you ";
$names[]=98.5;
$names[]=1.7E+23;
$num=count($names);
for ($i=0;$i echo "$names[$i]
";
}
?>
It can be seen that the elements in an array are not necessarily of the same type , this is the "live" part of PHP arrays.
Using objects makes it easier for programmers to maintain and makes programs more readable. Compared with other languages, PHP is much simpler. It only has categories, methods, attributes, extensions, etc.

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。

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。

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。

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)”。


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