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Constants In PHP

In this article, we will discuss constant in PHP.

Software Requirement

Before you start reading this tutorial, you should make sure that

In order to understand this tutorial, you should know about identifiers in programming language and their purpose.

In computer language, constant is an identifier whose value cannot be changed during the execution of the program.

In PHP, a constant should always start with an alphabet or underscore (_).

We can set the value of constant using "define" function. Here is the syntax

define(constant_name, constant_value,is_case_insensitive);

First parameter is the name of the constant
Second parameter is the value of the constant.
Third one is the optional parameter which specifies if the constant name is case insensitive or not. By default, the value is false which means that the constant name is case sensitive.

<?php
define("PIE", "3.14", true);
echo pie
?>

This above code will display "3.14"

<?php
define("PIE", "3.14");
echo pie
?>

And the code above will throw an error – "Notice: Use of undefined constant pie " as the constant is case sensitive

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