# PHP Constants

PHP Constants are the identifiers that once defined, cannot be modified. PHP Constants can either be defined using a define() function or a const keyword. Like PHP Variables, PHP Constants name can only be started with a letter or an underscore only. PHP constants are globally defined only.

PHP define() function:

Syntax:

define(name, value, case-insensitive)

• Name: This parameter is used to specify the name of the constant.
• Value: This parameter is used to specify the value of the constant.
• Case-insensitive: This parameter is used to specify whether the constant is to be case-sensitive or case insensitive. It can take two values: True or False. By default the value is False, i.e, the constant is understood to be case sensitive.

PHP const keyword:
PHP const keyword is a faster method to define constants as it can only define case sensitive constants and only at the compile time.

Example 1: Defining PHP Constants using define() function

<!DOCTYPE html> <html> <body>   <?php define("Name", "Shanaya"); echo Name; ?>   </body> </html>

Example 2: Defining PHP Constants using const keyword

<!DOCTYPE html> <html> <body>   <?php const MESSAGE="Hello World"; echo MESSAGE; ?>   </body> </html>