define and constants

In PHP, the define() function is used to define a constant. A constant is a value that cannot be changed once it has been set. Constants are global in scope, which means they can be accessed from anywhere in your PHP code.

Here is an example of how to use the define() function to define a constant:

define("MAX_WIDTH", 100);
echo MAX_WIDTH;  // prints 100

The define() function takes two arguments: the name of the constant and the value to be assigned to it. The constant name must be written in uppercase and it cannot be defined using a $ symbol like a variable.

You can also define constants using the const keyword, which has been available since PHP 5.3.0. Here is an example of using the const keyword to define a constant:

const MAX_HEIGHT = 200;
echo MAX_HEIGHT;  // prints 200

Both define() and const are used to define constants in PHP, but const has some additional benefits. It is more intuitive to use, and it is also faster and more efficient because it is resolved at compile-time rather than runtime.