PHP Constants

Values that never change.

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A constant is a name for a value that cannot change during the script.

define("SITE_NAME", "CodesInTech");
const TAX_RATE = 0.18;
Constants have no $ and are global automatically.
By convention, constant names are UPPERCASE.

PHP also has "magic constants" like __LINE__, __FILE__ and __DIR__.

Key Takeaways: PHP Constants

Mastering PHP Constants helps you write clean and reliable PHP code. Follow standard conventions, test edge cases, and keep logic simple. Try running the code example below and complete the exercises to build confidence.

PHP Constants Code Example

PHP

<?php
define("SITE_NAME", "CodesInTech");
const TAX_RATE = 0.18;

$price = 1000;
echo SITE_NAME . "<br>";
echo "Total with tax: " . $price * (1 + TAX_RATE) . "<br>";
echo "This is line " . __LINE__;

Output

CodesInTech
Total with tax: 1180
This is line 8

Run this example on your own computer. The "Get Started" lesson shows how to set it up.

PHP Constants Practice Exercises

Check what you learned in “PHP Constants”.

/ 2 solved

Fill in the blank

Define a constant.

("SITE_NAME", "CodesInTech");

✓ Correct! Not quite. Try again.

Multiple choice

Do constants start with $?

No Yes Only inside classes Only in PHP 8

✓ Correct! Not quite. Try again.

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PHP Constants

💡 Key Takeaways: PHP Constants

PHP Constants Code Example

PHP Constants Practice Exercises

Key Takeaways: PHP Constants