PHP Constants

In PHP, constants are identifiers that cannot be changed during the execution of the script. They are similar to variables, but they cannot be modified once they have been defined. Constants are often used to store values that are not likely to change, such as the name of a database or the path to a file.

Constants can be defined using the define() function or the const keyword. The syntax for defining a constant using the define() function is as follows:

define(name, value);

The name argument is the name of the constant, and the value argument is the value of the constant. The value of the constant can be any valid PHP expression.

The syntax for defining a constant using the const keyword is as follows:

const name = value;

The name and value arguments are the same as for the define() function.

Once a constant has been defined, it can be used anywhere in the script. For example, the following code defines a constant named PI and assigns it the value 3.14159:

define("PI", 3.14159);

The following code then uses the PI constant to calculate the circumference of a circle with a radius of 5:

$radius = 5;

$circumference = 2 * PI * $radius;

The circumference variable will now contain the value 31.4159.

Constants are a useful way to store values that are not likely to change. They can make your code more readable and easier to maintain.

Here are some of the rules for defining constants in PHP:

Constants must be defined before they are used.

Constants cannot be redefined.

Constants cannot be deleted.

Constants must be named using all uppercase letters.

Constants cannot contain spaces or special characters.

I hope this helps!