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:

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:

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 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:

/* 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.

4.2 Boolean type

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

".$b."
".$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.

4.4 Floating point type

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