PHP Constants

A constant is a name or an identifier for a simple value. A constant value cannot change during
the execution of the script. By default a constant is case-sensitive. By convention, constant
identifiers are always uppercase. A constant name starts with a letter or underscore, followed by
any number of letters, numbers, or underscores. If you have defined a constant, it can never be
changed or undefined.

To define a constant you have to use define() function and to retrieve the value of a constant,
you have to simply specifying its name. Unlike with variables, you do not need to have a
constant with a $. You can also use the function constant() to read a constant's value if you
wish to obtain the constant's name dynamically.

Example:

<?php  

define("MINSIZE", 50); 

echo MINSIZE; 

echo constant("MINSIZE"); // same thing as the previous line 

?> 

Output:

5050

Example:2

<?php  

define("MINSIZE", 50); 

echo MINSIZE;

echo "<br/>"; 

echo constant("MINSIZE"); // same thing as the previous line 

?> 

Output:

50

50

IMPORTANT

Only scalar data (boolean, integer, float and string) can be contained in constants.