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  • 2.1 PHP Data Types
  • 2.2 PHP Strings
  • 2.3 PHP Numbers
  • 2.4 PHP Math
  • 2.5 PHP Constants
  • 2.6 PHP Casting
  • 2.7 PHP Magic Constants
    •
  • 1.1 PHP Intro
  • 1.2 PHP Install
  • 1.3 PHP Syntax
  • 1.4 PHP Comments
  • 1.5 PHP Variables
  • 1.5.1 Variables Scope
  • 1.6 PHP Echo / Print
    •
  • 2.1 PHP Data Types
  • 2.2 PHP Strings
  • 2.3 PHP Numbers
  • 2.4 PHP Math
  • 2.5 PHP Constants
  • 2.6 PHP Casting
  • 2.7 PHP Magic Constants
    •
  • 3.1 PHP Operators
  • 3.2 PHP If Else Elseif
  • 3.3 PHP Switch
  • 3.4 PHP Loops
  • 3.4.1 While Loop
  • 3.4.2 Do While Loop
  • 3.4.3 For Loop
  • 3.4.4 Foreach Loop
  • 3.4.5 Break/Continue
  • 3.5 PHP Functions
    •
  • 4.1 PHP Arrays
  • 4.1.1 Indexed Arrays
  • 4.1.2 Associative Arrays
  • 4.1.3 Multidimensional Arrays
  • 4.1.4 Sorting Arrays
  • 4.2 PHP Superglobals
  • 4.2.1 $GLOBALS
  • 4.2.2 $_SERVER
  • 4.2.3 $_REQUEST
  • 4.2.4 $_POST
  • 4.2.5 $_GET
  • 4.3 PHP RegEx
    •
  • 5.1 PHP Form Handling
  • 5.2 PHP Form Validation
  • 5.3 PHP Form Required
  • 5.4 PHP Form URL / E-mail
  • 5.5 PHP Form Complete
    •
  • 6.1 PHP Date and Time
  • 6.2 PHP Include Files
  • 6.3 PHP File Handling
  • 6.4 PHP File Open/Read
  • 6.5 PHP File Create/Write
  • 6.6 PHP File Upload
  • 6.7 PHP Cookies
  • 6.8 PHP Sessions
  • 6.9 PHP Filters
  • 6.10 PHP Filters Advanced
  • 6.11 PHP Callback Functions
  • 6.12 PHP JSON
  • 6.13 PHP Exceptions
    •
  • 7.1 PHP What is OOP
  • 7.2 PHP Classes / Objects
  • 7.3 PHP Constructor
  • 7.4 PHP Destructor
  • 7.5 PHP Access Modifiers
  • 7.6 PHP Inheritance
  • 7.7 PHP Class Constants
  • 7.8 PHP Abstract Classes
  • 7.9 PHP Interfaces
  • 7.10 PHP Traits
  • 7.11 PHP Static Methods
  • 7.12 PHP Static Properties
  • 7.13 PHP Namespaces
  • 7.14 PHP Iterables
    •
  • 8.1 MySQL Database
  • 8.2 MySQL Connect
  • 8.3 MySQL Create DB
  • 8.4 MySQL Create Table
  • 8.5 MySQL Insert Data
  • 8.6 MySQL Get Last ID
  • 8.7 MySQL Insert Multiple
  • 8.8 MySQL Prepared
  • 8.9 MySQL Select Data
  • 8.10 MySQL Where
  • 8.11 MySQL Order By
  • 8.12 MySQL Delete Data
  • 8.13 MySQL Update Data
  • 8.14 MySQL Limit Data
    •
  • 9.1 PHP XML Parsers
  • 9.2 PHP SimpleXML Parser
  • 9.3 PHP SimpleXML - Get
  • 9.4 PHP XML Expat
  • 9.5 PHP XML DOM
    •
  • 10.1 AJAX Intro
  • 10.2 AJAX PHP
  • 10.3 AJAX Database
  • 10.4 AJAX XML
  • 10.5 AJAX Live Search
  • 10.6 AJAX Poll
  • My Poll
    •

    • 2.5 PHP Constants

    Constants are like variables except that once they are defined they cannot be changed or undefined.

    PHP Constants

    • A constant is an identifier (name) for a simple value. The value cannot be changed during the script.
    • A valid constant name starts with a letter or underscore (no $ sign before the constant name).
    • Note: Unlike variables, constants are automatically global across the entire script.

    Create a PHP Constant

    To create a constant, use the define() function.

    Syntax

    define(name, value, case-insensitive)
    • Parameters:
      • name: Specifies the name of the constant
      • value: Specifies the value of the constant
      • case-insensitive: Specifies whether the constant name should be case-insensitive. Default is false
    Example 1: PHP Constants - Create a PHP Constant part 1

    Create a constant with a case-sensitive name:

    <?php
define("GREETING", "Welcome to W3Schools.com!");
echo GREETING;
?>
    Example 2: PHP Constants - Create a PHP Constant part 2

    Create a constant with a case-insensitive name:

    <?php
define("GREETING", "Welcome to W3Schools.com!", true);
echo greeting;
?>

    PHP Constant Arrays

    In PHP7, you can create an Array constant using the define() function.

    Example 3: PHP Constants - Create an Array constant:
    <?php
define("cars", [
  "Alfa Romeo",
  "BMW",
  "Toyota"
]);
echo cars[0];
?>

    Constants are Global

    Constants are automatically global and can be used across the entire script.

    Example 4: PHP Constants - Constants are Global

    This example uses a constant inside a function, even if it is defined outside the function:

    <?php
define("GREETING", "Welcome to W3Schools.com!");

function myTest() {
  echo GREETING;
}
 
myTest();
?>

    PHP Fundamentals course home
    Module 2. Data Types

    Navigate this module
  • 2.1 PHP Data Types
  • 2.2 PHP Strings
  • 2.3 PHP Numbers
  • 2.4 PHP Math
  • 2.5 PHP Constants
  • 2.6 PHP Casting
  • 2.7 PHP Magic Constants
    •

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    Module 2 quiz

    Example files created in this module:
    PHP String PHP Integer PHP Float PHP Array PHP Object PHP NULL Value PHP String Functions - strlen() Return the Length of a String PHP String Functions - str_word_count() Count Words in a String PHP String Functions - strrev() Reverse a String PHP String Functions - strpos() Search For a Text Within a String PHP String Functions - str_replace() Replace Text Within a String PHP Numbers - Integers is_int() PHP Numbers - Floats is_float() PHP Numbers - Check if a numeric value is finite PHP Numbers - Invalid calculation will return a NaN value: PHP Numbers - Check if the variable is numeric PHP Numbers - Cast float to int PHP Constants - Create a PHP Constant part 1 PHP Constants - Create a PHP Constant part 2 PHP Constants - Create an Array constant: PHP Constants - Constants are Global PHP Casting - Cast to String PHP Casting - Cast to Integer PHP Casting - Cast to Float PHP Casting - Cast to Boolean PHP Casting - Cast to Array part 1 PHP Casting - Cast to Array part 2 PHP Casting - Cast to Object part 1 PHP Casting - Cast to Object part 2 PHP Casting - Cast to NULL