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+.. _arduino-define:
+
+Define
+======
+
+``#define`` is a useful C component that allows the programmer to
+give a name to a constant value before the program is compiled.
+Defined constants in arduino don't take up any program memory space
+on the chip. The compiler will replace references to these
+constants with the defined value at compile time.
+
+
+
+This can have some unwanted side effects though, if for example, a
+constant name that had been #defined is included in some other
+constant or variable name. In that case the text would be replaced
+by the #defined number (or text).
+
+
+
+In general, the *`const <http://arduino.cc/en/Reference/Const>`_*
+keyword is preferred for defining constants and should be used
+instead of #define.
+
+
+
+Arduino defines have the same syntax as C defines:
+
+
+
+Syntax
+------
+
+``#define constantName value``
+
+
+
+Note that the # is necessary.
+
+
+
+Example
+-------
+
+::
+
+    #define ledPin 3
+    // The compiler will replace any mention of ledPin with the value 3 at compile time.
+
+
+
+Tip
+---
+
+There is no semicolon after the #define statement. If you include
+one, the compiler will throw cryptic errors further down the page.
+
+
+
+::
+
+    #define ledPin 3;    // this is an error 
+
+
+
+Similarly, including an equal sign after the #define statement will
+also generate a cryptic compiler error further down the page.
+
+
+
+::
+
+    #define ledPin  = 3  // this is also an error 
+
+
+
+See
+---
+
+
+-  `const <http://arduino.cc/en/Reference/Const>`_
+-  `Constants <http://arduino.cc/en/Reference/IntegerConstants>`_
+