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+.. _arduino-const:
+
+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
+*`variable scoping <http://arduino.cc/en/Reference/Scope>`_* 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
+*`#define <http://arduino.cc/en/Reference/Define>`_*.
+
+
+
+Example
+-------
+
+::
+
+    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
+    
+
+**#define** or **const**
+------------------------
+
+You can use either **const** or **#define** for creating numeric or
+string constants. For
+`arrays <http://arduino.cc/en/Reference/Array>`_, you will need to
+use **const**. In general *const* is preferred over *#define* for
+defining constants.
+
+
+
+See also:
+
+
+-  `#define <http://arduino.cc/en/Reference/Define>`_
+-  `volatile <http://arduino.cc/en/Reference/Volatile>`_
+