Reference   Language | Libraries | Comparison | Changes

Arduino Reference

Arduino programs can be divided in three main parts: structure, values (variables and constants), and functions.


An Arduino program run in two parts:

setup() is preparation, and loop() is execution. In the setup section, always at the top of your program, you woiuld set pinMode, initialize serial communication, etc. The loop section is the code to be executed -- reading inputs, triggering outputs, etc.

Control Structures

Comparison Operators

  • == (equal to)
  • != (not equal to)
  • < (less than)
  • > (greater than)
  • <= (less than or equal to)
  • >= (greater than or equal to)

Boolean Operations

  • && (and)
  • || (or)
  • ! (not)

Further Syntax

  • ; (semicolon)
  • {} (curly braces)
  • // (single line comment)
  • /* */ (multi-line comment)
  • #define


Variables are expressions that you can use in programs to store values, like e.g. sensor reading from an analog pin. They can have various types, which are described below.


Constants are labels for certain values which are preset in the Arduino compiler. You do not need to define or initialize constants. Arduino includes the following pre-defined constants.


Digital I/O

Analog I/O

Advanced I/O

  • shiftOut(dataPin, clockPin, bitOrder, value)
  • unsigned long pulseIn(pin, value)



Random Numbers

External Interrupts

These functions allow you to trigger a function when the input to a pin changes value.

Serial Communication

Used for communication between the Arduino board and a computer or other devices. This communication happens via the Arduino board's serial or USB connection and on digital pins 0 (RX) and 1 (TX). Thus, if you use these functions, you cannot also use pins 0 and 1 for digital i/o.

Reference Home

Corrections, suggestions, and new documentation should be posted to the Forum.

The text of the Arduino reference is licensed under a Creative Commons Attribution-ShareAlike 3.0 License. Code samples in the reference are released into the public domain.