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authorHanna Mendes Levitin <hanna@anomaly-3.local>2010-12-01 03:37:07 -0600
committerHanna Mendes Levitin <hanna@anomaly-3.local>2010-12-01 03:37:07 -0600
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+.. highlight:: cpp
+
+.. _lang-const:
+
+``const``
+=========
+
+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 same rules of
+:ref:`variable scoping <lang-scope>` that govern other
+variables. This, and the pitfalls of using :ref:`#define
+<lang-define>`, often makes using the ``const`` keyword a superior
+method for defining constants than ``#define``.
+
+Example
+-------
+
+::
+
+ // this defines a variable called "pi", which cannot be changed:
+ const float pi = 3.14;
+ float x;
+
+ // ....
+
+ x = pi * 2; // it's fine to find the value of a const variable
+
+ 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 :ref:`arrays <lang-array>`\ , you will need
+to use ``const``. In general, ``const`` is preferred over ``#define``
+for defining constants.
+
+See Also
+--------
+
+- :ref:`#define <lang-define>`
+- :ref:`volatile <lang-volatile>`
+
+
+.. include:: cc-attribution.txt