Page 65 - Programming the Photon Getting Started With the Internet of Things

Arrays are a way of containing a list of different values. This is unlike what we have
learned before, where variables contained only a single value, usually an int data type. In

contrast to this, an array contains a list of values, and you can easily access any one of
those values by its particular position in the array. In most programming languages, and in
fact computer science in general, the first value is always represented as a 0 rather than a
1; this means that the first variable is actually element zero. Here are some examples of
how to declare an array in your code:

int myValue[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 in myValue. In 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 of type char, one more element than your
initialization is required to hold the required null character.

Arrays are zero indexed—that is, referring to the array initialization earlier, 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 10 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 mem

ory 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) 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 your
program malfunctioning. This can also be a difficult bug to track down.

Strings

A string is a sequence of characters and a way for your Photon to deal with text. It is
highly unlikely that we would use strings within our code—possibly if you are using a

liquid crystal display (LCD) display, then a string might come into play.

All of the following are valid declarations for strings: