====== const keyword   ======

The **const** keyword stands for constant. It is a variable ''qualifier'' that modifies the behavior of the variable, making a variable "''read-only''". This means that the variable can be used just as any other variable of its type, but its value cannot be changed. You will get a compiler error if you try to assign a value to a **const** variable. 

Constants defined with the ''const'' keyword obey the rules of ''[[arduino:variable scope and qualifiers:Scope | variable scoping]]'' that govern other variables. This, and the pitfalls of using''#define'', makes the ''const'' keyword a superior method for defining constants and is preferred over using ''[[arduino:further_syntax:define |#define]]''. 

==== Example   ====
<code arduino>
const float pi = 3.14;
float x;

// ....

x = pi * 2;    // it's fine to use const's in math

pi = 7;        // illegal - you can't write to (modify) a constant

</code>
==== **#define** or **const**   ====

You can use either **const** or **#define** for creating numeric or string constants.  For [[arduino:data_types:Array|arrays]], you will need to use **const**. In general ''const'' is preferred over ''#define'' for defining constants.


See also:
*[[arduino:further_syntax:define | #define]]
*[[arduino:variable scope and qualifiers:Volatile]]
Source: arduino.cc