.. 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:: /arduino-cc-attribution.txt