Constants

Constants are like variables except that once they are defined they cannot be changed or undefined.A constant is an identifier (name) for a simple value. The value cannot be changed during the script.A valid constant name starts with a letter or underscore (no $ sign before the constant name).

Note: Unlike variables, constants are automatically global across the entire script.

Create a PHP Constant:-

To create a constant, use the define() function.

Syntax:-

define(name, value, case-insensitive)

Parameters:

1. name: Specifies the name of the constant
2. value: Specifies the value of the constant
3. case-insensitive: Specifies whether the constant name should be case-insensitive. Default is false

<?php
define("SCHOOL", "Welcome to s1school.blogspot.com");
echo SCHOOL;
?>

Constants are Global:-

Constants are automatically global and can be used across the entire script.

The example below uses a constant inside a function, even if it is defined outside the function:

<?php
define("SCHOOL", "Welcome to s1school.blogspot.com");

function myTest() {
    echo SCHOOL;
}
 
myTest();
?>