How to declare a constant in PHP?

@jasen_gottlieb 

In PHP, you can declare a constant using the define() function. The define() function takes two parameters: the name of the constant and its value. Here is an example:

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// Define a constant named PI with the value 3.14159
define('PI', 3.14159);

In this example, the define() function creates a constant named PI with the value 3.14159. Once a constant is defined, it cannot be changed or redefined throughout the execution of the script.

You can then use the constant in your code by referencing its name, like this:

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// Output the value of the constant PI
echo PI;

This will output the value of the constant PI. You can also use constants in expressions, like this:

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// Calculate the area of a circle with radius 2 using the constant PI
$area = PI * 2 * 2;
echo $area;

This will output the area of the circle with radius 2, which is calculated using the constant PI.