Constant
- A Constant is value the cannot be altered with in the normal execution of the program.
- A constant is a case-sensitive and by convention the constants are always in upper case .
- Constant can have the global scope and can be called anywhere in the program .
- The constant starts with letters or underscore , followed by the numbers of letters , numbers ,or underscore .
Syntax :
define(name , value );
Example :
<?php
// Valid declaration
define(‘MY_PHP’ , ‘Constant with php’);
// Generate output
echo MY_PHP ;
// invalid declaration
define(’99PHP’ , ‘Constant with php’);
?>
Output :
Constant with php
Constant as Global Scope
<?php
function constant_global() {
echo MY_PHP;
}
constant_global();
?>
Same output as above .
Variables
- The variables are declared by dollar sign ($) followed by the name of variables , i.e alpha numeric characters along with underscore .
- It cannot be started with the number .
- Variables are case-sensitive , i.e $a and $A , both treated as different variables .
<?php
$var1 = ‘Learn Php’;
$var2 = ‘ with php interview questions ‘;
echo “$var1, $var2”; // outputs “Learn Php with php interview questions “
$1var = ‘Learn’; // invalid; starting with a number
$_4var = ‘php’; // valid; starting with an underscore
?>