.. highlight:: cpp

.. _lang-array:

Arrays
======

An array is a collection of variables that are accessed with an index
number. Arrays in the C++ programming language, in which the Maple is
programmed, can be complicated, but using simple arrays is relatively
straightforward.

.. contents:: Contents
   :local:

Creating (Declaring) an Array
-----------------------------

All of the methods below are valid ways to create (declare) an
array. ::

      int myInts[6];
      int myPins[] = {2, 4, 8, 3, 6};
      int mySensVals[6] = {2, 4, -8, 3, 2};
      char message[6] = "hello";

You can declare an array without initializing it, as with myInts.  In
the line referring to myPins, we declare an array without explicitly
choosing a size.  The compiler counts the elements and creates an
array of the appropriate size.

Finally, you can both initialize and size your array, as in
mySensVals. Note that when declaring an array with elements of type
char, one more element than your initialization is required, to hold
the required `null character <http://en.wikipedia.org/wiki/Null-terminated_string>`_.


Accessing an Array
------------------


.. compound::

   Arrays are **zero indexed**; that is, referring to the array
   initialization above, the first element of the array is at index 0,
   hence ::

      mySensVals[0] == 2;
      mySensVals[1] == 4

   and so forth.

It also means that in an array with ten elements, index nine is the
last element. Hence::

    int myArray[10]={9,3,2,4,3,2,7,8,9,11};
         // myArray[9]    contains 11
         // myArray[10]   is invalid and contains random information (other memory address)

For this reason, you should be careful in accessing arrays.  Accessing
past the end of an array (using an index number greater than your
declared array size - 1) is reading from memory that is in use for
other purposes. Reading from these locations is probably not going to
do much except yield invalid data. Writing to random memory locations
is definitely a bad idea, and can often lead to unhappy results such
as crashes or program malfunction. This can also be a difficult bug to
track down.

Unlike Basic or Java, the C compiler does no checking to see if array
access is within legal bounds of the array size that you have
declared.


To assign a value to an array
-----------------------------
 ::

    mySensVals[0] = 10;


To retrieve a value from an array
---------------------------------

 ::

    x = mySensVals[4];


Arrays and ``for`` Loops
------------------------

Arrays are often manipulated inside :ref:`for loops <lang-for>`, where
the loop counter is used as the index for each array element. For
example, to print the elements of an array over the serial port, you
could do something like this::

    int i;
    for (i = 0; i < 5; i = i + 1) {
      SerialUSB.println(myPins[i]);
    }


Example
-------

For a complete program that demonstrates the use of arrays, see the
Arduino `Knight Rider example
<http://www.arduino.cc/en/Tutorial/KnightRider>`_\ (which will run
unmodified on the Maple).

Arduino Compatibility
---------------------

Arrays on Maple are identical those on Arduino.

See also
--------

-  :ref:`Storing arrays in FLASH memory <arm-gcc-attribute-flash>`



.. include:: cc-attribution.txt
