What should you pay attention to when declaring a variable in php?

How to understand variables in php?

Variables in programs originate from mathematics and can be used in programming languages Store results or represent abstract concepts.

A simple understanding is that a variable is a container that temporarily stores values. It can store numbers, text, and some complex data (such as strings, complex permutations, etc.). Variables are at the core of the PHP language. This is the key to using php. (Recommended learning: PHP programming from entry to proficiency)

The value of the variable will change at any time during the running of the program. You can give a short and easy-to-remember name for a piece of data to be used in the program. , in addition it can save user input data and the results of feature operations. Summary variables are simple tools for tracking almost any type of information.

Variables in the php language

php data storage unit is variables and constants to store various types of data. PHP is a weakly typed language. Before using variables There is no need to declare variables. Variables are created when assigning values. This reason makes PHP syntax very different from C language and Java (strongly typed language).

Declaration and attention of PHP variables

When declaring variables in PHP, you must use a dollar sign "$" followed by the variable name, and then use the assignment operation (=) Assign a value to a variable. As shown in the figure

#The variable name cannot start with a number.

PHP variables have a certain scope of use after they are declared. Most PHP variables are not declared in functions. Only a separate range from the declaration point to the end of the file is used. This separate range can be used on a page. Used in all php modes.

also includes include and require import files. During the variable usage period, you can use unset() to release the specified variable, use isset() to check whether the variable is set, and use isempty() to check whether the variable is empty.

php variable naming rules

1. Case sensitive

$A and $a$ are two different variables, (system built-in structure and keywords, user-defined class and function names are case-sensitive).

2. The variable starts with the $ symbol, followed by the name of the variable.

3. Variable names must start with letters or underscores and cannot start with numbers.

4. Variable names can only contain alphanumeric characters and underscores (A-z, 0-9 and _)

If the variable is composed of letters, all lowercase is usually used as the variable name. If the variable is made up of multiple characters, use all lowercase letters for the first letter and capitalize each subsequent letter. For example: $aaaBbbCcc style, it is recommended that you use this variable naming method.

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