Constants are like a variable, except that their value never changes during execution once defined.
- The constant value is immutable.
- Constant within a script is accessible to any area; however, they can be scalar values.
- Constant names are case-sensitive, and they also follow the same naming requirements like variables, except the leading $.
- It is considered best practice to define constants using only upper-case names.
Constant Definition in PHP
PHP define() function defines a constant.
Syntax:
bool define ( string $name , mixed $value [, bool $case_insensitive = false ] )| Parameters | Description |
|---|---|
| name | The name of the constant. |
| value | The value of the constant; only scalar and null values are allowed. Scalar values are an integer, float, string or Boolean values. |
| case_insensitive | If set to TRUE, the constant will be defined case-insensitive. |
Example:
<?php
define("EMAIL", "[email protected]"); // Valid constant name
echo EMAIL; // Displays "[email protected]"
define("myCon", true);
if (myCon) { } // Evaluates to true
define("ONECONSTANT", "some value"); // Invalid constant name
define("CONSTANT", "Hello world.");
echo CONSTANT; // outputs "Hello world."
echo Constant; // outputs "Constant" and issues a notice.
define("GREETING", "Hello world.", true);
echo GREETING; // outputs "Hello world."
echo Greeting; // outputs "Hello world."
?> How to create and use PHP constants
String Concatenation in PHP
String Concatenation is a process of adding two strings. We can echo more than one variable or constant on a line using a concatenation operator ('.'), e.g.
<?php
$like = "I like php";
$num = 7;
echo $like . $num;
echo "<p>";
echo $like . " " . $num;
echo "</p>";
echo "My favorite php version is $num";
?>