This article details the types of constants in Arduino programming
Overview
They are predefined expressions in the Arduino language, used to make the sketch easier to read.
HIGH | LOW
As you may have read in the Digital Functions articles, when reading or writing to a digital pin, there are only two possible values a pin can take: HIGH and LOW.
The meaning of HIGH and LOW depends on whether the pin is declared as an INPUT or an OUTPUT. Visit the articles on digital functions to learn more.
true | false
the two constants used to represent truth and falsity are: 'true,' and 'false.'
False
Defined as 0.
True
Often defined as 1, but technically has a wider definition, and can be expanded to include any non-0 number. Both the true and false constants should be typed in lowercase letters, in contrast to the HIGH and LOW constants, among others.
LED_BUILTIN
Most Arduino boards have a pin connected to an on-board LED in series with a resistor. The constant LED_BUILTIN is the number of the pin to which the on-board LED is connected. Most boards have this LED connected to digital pin 13; however, to avoid confusion, I usually affirm this by examining a schematic of the board.
Integer Constants:
Numbers that are used directly in a sketch, whose value is replaced with the assigned variable at compile time.
Example:
number = 5 // 5 is an integer constant, so at any later time in the program where I reference 'number,' the compiler will replace that value with '5'
Note: integer constants can be written in a variety of forms and different base numbers (ie binary and hexadecimal)
Floating-Point Constants:
Similar to integer constants with the exception that they refer to numbers containing decimal points.
Example:
number = .001; // .001 is a floating-point constant