Definition of constants in PHP

1. the user-defined constant * must be defined using the define () function *. after the definition, its value cannot be changed *. the constant name is used directly, and $ s cannot be added in front like a variable. for example: define (& quot; PI & quot;, 3.14); defines a constant $ areaPI * R; calculates the area of the circle define (& quot ;... syntaxHig

1. Custom constants
* Must be defined using the define () function
* After definition, the value cannot be changed.
* The constant name is used directly. you cannot add $ s in front of a variable.
For example: define ("PI", 3.14); defines a constant
$ Area = PI * R; calculate the area of the circle
Define ("URL", "http://www.ybldcc.com ");
Echo "My website is:". URL;
2 System constants:
FILE: php program FILE name
LINE: Number of PHP program files
PHP_VERSION: version number of the current parser
PHP_ OS: name of the operating system for executing the current PHP version
Author: "ITeamsky-Yang Bo's technical space"