Understanding Constants in PHP: Defining and Using Constants in PHP Programming

In PHP, a constant is a named value that cannot be changed during the execution of a script. It is a type of variable whose value remains constant throughout the script's execution, and it cannot be redefined or modified once it is defined. Constants are useful for storing values that should not be changed, such as configuration settings, mathematical or scientific constants, and other fixed values.

<?php
   define("PROGRAM","PHP");
?>

In this example, a constant named "PROGRAM" is defined with the value of PHP. Once defined, this constant can be used throughout the script without being redefined or modified.

Some key points to note about constants in PHP:

Constants are case-sensitive by default, meaning that "PROGRAM" and "program" would be treated as separate constants. However, you can make constants case-insensitive by setting the third parameter of the define() function to true.
Constants can only contain scalar data types such as integers, floating-point numbers, strings, or booleans. They cannot contain arrays or objects.
Constants are global, meaning that they can be accessed from any part of the script, including functions and classes.
Constants cannot be redefined or modified once they are defined using the define() function. Attempting to redefine a constant will result in a warning or an error, depending on the error reporting settings of your PHP environment.
Constants are not prefixed with a dollar sign ($), unlike variables in PHP.
Constants are typically written in uppercase letters with underscores (_) to separate words for better readability, following the naming conventions for constants.

Using constants can help improve code readability, maintainability, and reduce the risk of accidental modifications to fixed values in your PHP scripts. They are widely used in PHP programming for defining configuration settings, constant values, and other fixed values that should not be changed during script execution.

Sample Code

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>constants</title>
</head>
<body>
  <?php 
    define("PROGRAM","PHP");
    define("VERSION","8.2");
    define("NAMES",["Ram","Sam","Ravi"]);

    echo "Welcome to ".PROGRAM. " Version (".VERSION.")";
    echo "<br> Name : ".NAMES[0];
  ?>
</body>
</html>

In this code, three constants are defined using the define() function:

PROGRAM with the value "PHP"
VERSION with the value "8.2"
NAMES with the value being an array ["Ram", "Sam", "Ravi"]

These constants are then used in the following ways:

PROGRAM and VERSION are used to concatenate strings and display a welcome message with the program name and version.
NAMES is used to access the first element ("Ram") of the array and display it as a name.

Notable points about this code:

Constants are defined using the define() function, followed by the constant name and its value.
Constants can be used like variables in strings by wrapping them in curly braces {} or concatenating them with strings using the dot (.) operator.
Constants can be used in expressions, assignments, and function arguments just like variables.
Constants are case-sensitive by default, so "PROGRAM" and "program" would be treated as separate constants.
Constants can hold scalar values such as strings, integers, floating-point numbers, and booleans, as well as arrays. However, the values of constants cannot be changed once they are defined.
Constants are typically written in uppercase letters with underscores (_) to separate words, following common naming conventions for constants in PHP.

Output