Variables and Constants

Variables:

• Variables store data.
• Start with $ symbol.
• Case-sensitive.

<?php
$name = "John";    // string
$age = 20;         // integer
echo "My name is $name and I am $age years old.";
?>

Output:

My name is John and I am 20 years old.

Rules for Variables:

1. Must start with $.
2. First character after $ must be a letter or underscore.
3. Cannot start with a number.
4. Case-sensitive ($Name and $name are different).

<?php
echo "This is PHP!"; // statement ends with ;
?>

Constants:

• Constants are like variables but cannot be changed once defined.
• Use define() or const.

<?php
define("SITE_NAME", "My Website");
echo SITE_NAME;

const PI = 3.14;
echo " Value of PI: " . PI;
?>

Output:

My Website
Value of PI: 3.14