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This article mainly introduces what are the PHP variable knowledge points, have a certain reference value, interested friends can refer to, I hope you can learn a lot after reading this article, the following let the editor take you to understand it.

1. Declaration and assignment of variables

Declaring a PHP variable must be represented by a dollar sign "$" followed by a variable name, and then use "=" to assign a value to the variable. As follows:

The characteristics of variables in 2.PHP

You have to start with $. For example, the variable an is to be written as $a, which is not a part of the variable name.

The first letter of a variable cannot start with a number. The variable name must begin with a letter or an underscore.

The names of variables are case-sensitive.

Variables do not use special symbols, Chinese, _ (underscore) is not a special symbol

Variable naming should be meaningful (variable name such as xxx,aaa,ccc)

The correct naming is as follows:

3.echo display variable instruction

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

PHP comment

Annotation has many functions: marking the key points, easy to find, easy to forget for a long time, and improving work efficiency.

/ /, # # means one-line comments, usually used more.

/ * Multiline comments * / indicates multiline comments

Examples are as follows:

/ * here is smoking harmful to health * / 4.PHP variable data type

4.1 Integer

Integers are integers, which can be positive or negative.

4.2 Boolean type

Boolean 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:

Declare in single quotation marks

Declare in double quotation marks

Declare with a character delimiter

Where the character delimiter is used when you need to enter a very large string.

Note when declaring with character delimiters:

Write three less than signs after the equal sign of the variable

If the double quotation marks are replaced by single quotation marks, the output result is: $a Chinese net, not.

Insert a variable in double quotation marks. If there are English or Chinese characters after the variable, it will concatenate the character with the variable and treat it as a whole variable.

Adding special characters after the variable can solve the problem:

Or instead of realistic special symbols, you can wrap variables in curly braces:

Double quotation marks and single quotation marks can be inserted into each other:

4.4 floating point type

Floating point is the decimal in mathematics. Valid values range from 1.8E-308 to 1.8E+308. Floating-point numbers are more accurate than integer data types.

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