In computer programming, a constant is an identifier with an associated value which cannot be altered by the program during normal execution – the value of the constant is, well, constant.
A constant is an identifier (name) for a simple value. As the name suggests, that value cannot change during the execution of the script. A constant is case-sensitive by default. By convention, constant identifiers are always uppercase..
Constants are used when you want to prevent changes to data in a program. This usually happens in larger programs, with multiple programmers. Constants also provide a measure of security, especially in web-based applications. In lower-level languages, constants can provide more efficient use of memory than variables.
Below is an example of declaring a constant in PHP:
<?php # this file is used to demonstrate constants in PHP define("SCHOOL_YEAR", "2016 - 2017"); # for the remainder of the running of this program, the value of SCHOOL_YEAR will be 2016 - 2017 # If we wanted to CALL (use) a constant, we might use the following syntax: note the lack of a $ symbol echo "The school year is " . SCHOOL_YEAR; ?>
- Define the terms: variable, constant, operator, object.