An exciting and easy-to-remember summary of PHP variable knowledge (details)

This article summarizes the basic summary of PHP variables, including the declaration of PHP variables and the data types of variables. As a learning summary, I hope it will be helpful to everyone!

1. Declaration and assignment of variables

To declare PHP variables, you must use a dollar sign "$" followed by the variable name. means, and then use "=" to assign a value to this variable. As shown below:

<?php
$a = 1;
$b = 2;
$c = 3;
?>

2. Characteristics of variables in PHP

• must start with $. If variable a is written as $a, $ is not part of the variable name.

• The first letter of a variable cannot start with a number. Variable names must start with a letter or underscore.

• Variable names are case-sensitive.

• Do not use special symbols or Chinese characters for variables. _ (underscore) is not considered a special symbol.

• Variable names must have Meaning (variable names like xxx, aaa, ccc)

The correct naming is as follows:

<?php
$name = "PHP中文网";                  // 变量名为：name，变量值为：PHP中文网
$url = "http://www.php.cn/";       // 变量名为：url，变量值为：http://www.php.cn/
$Url = "http://www.bilibili.com/";   // 变量名为：Url，变量值为：http://www.bilibili.com/
$_str = "阿泽不抽烟";        // 变量名为：_str，变量值为：阿泽不抽烟
?>

3.echo display variable command

echo is a command commonly used in PHP for output and display functions. You can use it to display any visible characters, for example:

<?php
$aze = 10086;
echo $aze;
?>

PHP comments

Comments have many functions: marking key points, easy to find, easy to forget after a long time, improve Work efficiency.

// and ## represent single-line comments, usually // is used more often.

/* Multi-line comments */ indicates multi-line comments
Examples are as follows:

<?php
//这段是单行注释
$aze = 10086;
echo $aze;
?>

/* 
这里是PHP中文网
吸烟有害身体健康
 */

4.PHP variable data type

4.1 Integer type

The integer type is an integer, which can be a positive number or a negative number.

<?php
//声明变量 整数int
//$int = 1000;
echo $zhengshu;
?>

4.2 Boolean type

The Boolean type has only two values: true(true) / false (False)

<?php
$buer = true;
$bool = false;
?>

4.3 String

A string is a continuous sequence of characters. In PHP, there are three ways to define a string:

• Use single quotes to declare

• Use double quotes to declare

• Use character delimiters to declare

Among them, the character delimiter is used when a very large string needs to be entered.

Be careful when declaring with character delimiters:

Write three less than signs (<<<) after the equal sign after the variable, and then < Write characters after ;<< (English uppercase characters are recommended). As in the following example: QWE. Then wrap the line and write any characters you want. After writing, top line. At the beginning of the line, write the characters following <<< and a semicolon.

<?php
//双引号方式声明字符串
$a = "好好学习";  
//单引号方式声明字符串
$b = &#39;天天向上&#39;;     
 //用字界符声明字符串
$c = <<<QWE
url：http://www.php.cn/
QWE;
echo $a."<br>".$b."<br>".$c;
?>

The difference between single quotes and double quotes when declaring strings:

• 1. Double quotes parse variables, single quotes do not parse variables.

• 2. Insert the variable inside the double quotes. If there are English or Chinese characters behind the variable, it will splice the character and the variable together and treat it as a whole variable. Be sure to separate the variables with special characters, such as spaces.

• 3. If you insert a variable within double quotes and do not want spaces behind it, you can wrap the variable in braces.

• 4. Double quotes parse escape characters, single quotes do not parse escape characters. However, single quotes can parse \' and \

• ## 5. Single quotes are more efficient than double quotes. Use single quotes as much as possible

• 6 .Double numbers and single quotes can be inserted into each other! ! ! Insert single quotes between double quotes, insert variables between single quotes, and the variable will be parsed.

• 7. (

  .) points are used to splice strings.

• 8. Treat the delimiter declaration string as having the same function as double quotes.

Example:

<?php
$a = &#39;PHP&#39;;
$b = "$a中文网 ";
echo $b;
?>

If the double quotes are replaced with single quotes, the output result will be: $a Chinese website, not PHP Chinese website.

<?php
$a = &#39;php中文网&#39;;
$b = "$axxxx";
echo $b;
?>

Insert a variable within double quotes. If there are English or Chinese characters behind the variable, it will concatenate the character and the variable and treat it as a whole variable.

This can be solved by adding special characters after the variable:

<?php
$a = &#39;php中文网&#39;;
$b = "$a xxxx";
echo $b;
?>

Or if you don’t want to use special characters, you can wrap the variable in braces:

<?php
$a = &#39;php中文网&#39;;
$b = "{$a}xxxx";
echo $b;
?>

Double quotation marks and single quotes can be interpolated with each other:

<?php
$a = &#39;东海&#39;;
$b = "福如&#39;$a&#39;,寿比南山";
echo $b;
?>

Insert a single quote between the double quotes, insert a variable between the single quotes, and the variable will be parsed.

When multiple strings are spliced ​​together, you can use dots (.) to splice the strings.

<?php$a = &#39;PHP&#39;;
$b = "中文网 ";
$c =&#39;young&#39;;
$d =&#39;beautiful&#39;;
echo $a.$b.$c.$d;
?>

4.4 Floating point type

Floating point type is also the decimal in mathematics. Valid values ​​range from 1.8E-308 to 1.8E 308. Floating point numbers have higher precision than integer data types.

<?php
$a = 10086.0326;
echo $a;
$b = 0.0326;
var_dump($b);
?>

Recommended learning: "

PHP Video Tutorial"

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