.. highlight:: cpp

.. _arduino-arithmetic:

Addition, Subtraction, Multiplication, & Division
=================================================

Description
-----------

These operators return the sum, difference, product, or quotient
(respectively) of the two operands. The operation is conducted using
the data type of the operands, so, for example, ``9 / 4`` gives ``2``
since 9 and 4 are ints.

This also means that the operation can overflow if the result is
larger than that which can be stored in the data type (e.g. adding 1
to an :ref:`arduino-int` with the value 2147483647 gives
-2147483648). If the operands are of different types, the "larger"
type is used for the calculation.  

(The specifics of these rules are beyond the scope of this
documentation; for more information, see `The C++ Programming Language
<http://www2.research.att.com/~bs/3rd.html>`_\ , by Bjarne
Stroustroup, Appendix C, especially §§C.4-C.6, or `this WikiBooks
entry on C++ type conversion
<http://en.wikibooks.org/wiki/C%2B%2B_Programming/Programming_Languages/C%2B%2B/Code/Statements/Variables/Type_Casting#Automatic_type_conversion>`_\
.  For more information on how computers represent integers, see the
Wikipedia page on `two's complement
<http://en.wikipedia.org/wiki/Two's_complement>`_\ ).

If one of the numbers (operands) are of the type **float** or of type
**double**, floating point math will be used for the
calculation.

Examples
--------

 ::

    y = y + 3;
    x = x - 7;
    i = j * 6;
    r = r / 5;


Syntax
------

 ::

    result = value1 + value2;
    result = value1 - value2;
    result = value1 * value2;
    result = value1 / value2;


Parameters:
-----------

**value1**: any numeric variable or constant

**value2**: any numeric variable or constant


Arduino Compatibility Note
--------------------------

Since the STM32 processor on the Maple is a 32-bit machine, the int
type overflows at a much higher value on Maple than on Arduino.  In
particular, on Maple, ints do not overflow (become negative) until
they reach 2,147,483,648; on the Arduino, they overflow at 32,767.
Because of this, programs running on Maple are much less likely to run
into overflow issues.


Programming Tips:
-----------------

- Know that :ref:`integer constants <arduino-integerconstants>`
  default to :ref:`int <arduino-Int>`, so some constant calculations
  may overflow (e.g., 200000 * 5000000 will yield a negative result).

- Choose variable sizes that are large enough to hold the largest
  results from your calculations.

- Know at what point your variable will "roll over" and also what
  happens in the other direction e.g. (0 - 1) for unsigned arithmetic,
  or (0 - -2,147,483,648) for signed arithmetic.

- For math that requires fractions, float variables may be used, but
  be aware of their drawbacks: large size and slow computation speeds
  (the STM32 has no floating point hardware, so all floating point
  calculations have to be done in software).

- Use the cast operator e.g. (int)myFloat to convert one variable type
  to another on the fly.


See Also
--------

- `libmaple_types.h <http://github.com/leaflabs/libmaple/blob/master/libmaple/libmaple_types.h>`_