What are the differences between php variable and constant naming?

Differences in naming php variables and constants: 1. The variable name needs to be modified with the dollar sign "$"; there is no dollar sign before the constant name. 2. Variable names are generally lowercase. When they consist of multiple words, the first letter of the first word is lowercase, and the first letter of the remaining words is uppercase; while constant names are generally all uppercase.

The operating environment of this tutorial: windows7 system, PHP7.1 version, DELL G3 computer

What are php constants?

The so-called constant is a quantity that cannot be changed. Once a PHP constant is defined, it cannot be changed or undefined. This is the official explanation and the most authoritative explanation. PHP constants are usually used to store data that does not change and is not expected to change. The data can only be data of four scalar data types: integer (integer), floating point (decimal), string, Boolean (true /false).

Naming rules for PHP constants

The naming rules for PHP constants are similar to the naming rules for PHP variables but not exactly the same.

php constant name must be composed of letters, underscores, and numbers; it cannot start with a number; whether it is case-sensitive is specified when defining it; it is recommended to know the meaning when naming (you will know what it means when you see it), use English words are used as constant names, and it is recommended that all letters be capitalized (such as: PI)

The difference in naming php variables and constants:

Difference 1:

php variable names need to be modified with a dollar sign ($), php constant names do not need to be

Difference 2:

php variable names are recommended to be lowercase, consisting of multiple When words are formed, the first letter of the first word is lowercase, and the first letter of the remaining words is uppercase. It is recommended that PHP constant names be in all uppercase letters.

Other differences between variables and constants:

• Different definition methods: PHP variables have no defined keywords or functions. When assigning values, is defined when. PHP constants must be defined using the define() function.

• The meanings of values ​​are different: the value stored by PHP variables can be changed, while the value stored by PHP constants cannot be changed.

• Scope is not used: PHP variables are defined outside all functions and have global scope; when defined within functions, they have local scope. PHP constants are generally defined outside all functions and have super-global scope.

• The data type range is different: PHP variables can be of any data type, while PHP constants can only be scalar types (integer, float/double, string, boolean).

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