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Arduino Programming: Variables, constants, and more

SCHOOL OF MAKING

Arduino Programming:

Variables, constants, and more

o you want your Arduino sketches

to look like they were written

by a professional? Use variables

and constants to self-document

your code.

In this series so far, you’ve learned

how to wire up some simple circuits and write

some Arduino code to interact with the circuit.

In this article, you’ll put aside the hardware and

learn about some fundamentals of the Arduino’s

language: variables, constants, and more. The goal

is to make you a better programmer and help you

deliver code that’s easier to read and for others

to understand.

Development languages such as Arduino’s

language provide mechanisms for managing data:

the information (numbers, Boolean values, strings)

that your sketches use to do their work. These

are implemented through Variable and Constant

language elements you’ve seen used in our

previous articles. Arduino devices have a limited

amount of memory and processing capabilities, and

you’ll want to make the best use of both in your

projects. As you code your Arduino sketches, there

are things you, as a developer, can do to manage

the memory profile for a sketch, and make the

sketch more readable at the same time.

VARIABLES

In the Arduino language, a variable is a pointer to

a memory location that stores a particular piece of

data. Variables are used to store data used by the

sketch, but also to increase code readability and

maintainability. Variables enable you to refer to a

data value by name rather than its value. As your

sketch runs, your code will store and retrieve data

by referring to the variable in expressions. Unlike

some other languages, in the Arduino language you

can’t use a variable until you’ve defined it. So to

define a variable, use the following expression:

Dig deeper into the data capabilities of the Arduino

language and make your sketches easier to read and maintain

D

DATA_TYPE VARIABLE_NAME;

Notice the semicolon at the end of the expression

• it’s required.
  In this example, DATA_TYPE defines the type of
  data that will be stored in the variable (supported
  types are array, bool, boolean, byte, char, double,
  float, int, long, short, string, unsigned char, unsigned
  int, unsigned long, word). The compiler allocates
  memory for the variable based on the data type
  you specify when you create the variable. The
  VARIABLE_NAME element of the expression defines
  the name you’ll use to refer to the variable in your
  code. A variable’s name can only have upper-
  case and lower-case letters, numbers, and the
  underscore character; using anything else will cause
  a compiler error.
  To create a variable called myInt that stores an
  integer value, use the following variable declaration:

John Wargo

@johnwargo

John is a professional

software developer,

writer, presenter,

father, husband, and

geek. He is currently a

Program Manager at

Microsoft, working on

Visual Studio Mobile

Center. You can find

him at johnwargo.com

Figure 1

The Arduino compiler will block some types of error before you

can upload your code the the board