⚑Definition of variables
⚑Type of variables
⚑Use of variables
Variables can exist in memory. Objects are constantly changing. We can imagine the memory as a street. There are many residents in the street. Each resident will have his own house number. This is like an address in the memory (a concept often mentioned in the C language). , we won’t discuss it much here), for one of the residents we can say it is Building 1, No. 1, or it can be said to be Wang Xiaoming’s home, using a name to replace an address. The number of people in Wang Xiaoming's family at a given time is a variable quantity. There may be 3 people at noon, only 1 person in the afternoon, and 5 people at night. Therefore, if we want to refer to a certain address in the memory, we can also call it A, or area. This is the variable.
Let’s demonstrate the declaration of variables in PHP.
Use "$" to add a variable name, such as $a, $var_name.
Note three points when declaring variables in PHP:
1. Variable names can only consist of English letters (A-Z, a-z), numbers (0-9) and underscores.
2. Variable names in PHP are case-sensitive, that is, $VAR_NAME and $var_name are two different variables.
3. A variable declaration or assignment must end with a semicolon (;).
The type definition of variables in PHP is very simple. Generally, there is no need to use keyword declarations, and it can be reflected in the form of assignment.
For example, declare an integer variable
$x=100;
Declare a character variable
$str="Iam a Chinese!" ;
Declare a Boolean variable
$bool=true;
Use variables in web pages.
For example, we want to display a sentence on the web page, "I am a Chinese", "I am 28 years old this year".

$age=28;
echo$str."
";
echo"I am this year".$ age."Age";
?>
Line 1 "
Line 2 $str="I am a Chinese"; defines a string variable str, whose value is "I am a Chinese".
Line 3 $age=28; defines an integer variable age and assigns it a value of 28.
Line 4 echo$str."
";, echo is the keyword used for output in PHP, and the content following it indicates that it is the content that needs to be output, that is, $str is the need Output variables, and the . after $str is a mark used to connect multiple variables or variables with general content. Here, a newline symbol
will be displayed after $str.
Line 5 echo "I am this year".$age."years old";, this sentence is understood in the same way as line 4. The sentence "I am 28 years old this year" is divided into three parts. "I am this year" is the first part. 28 is replaced by the variable $age. "Age" is the third part. They are connected by .
Line 6 "?>" indicates the end of this PHP file.
At this point, mission 1 is over. Up to now, you can express what you want to say on the web page in the form of PHP.
Author’s blog: http://walkbro.cnblogs.com/

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。

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。

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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