Function Tutorial for Arduino
Author:  Alexander Brevig

How to write and use functions for the Arduino.

So you want to write a Function for the Arduino?
Here is a little tutorial on how to write and use functions.

You will learn the basic syntax rules for c++ function declaration and definitions.

For this tutorial we will implement a function called blinkLED.
It will make the LED in question blink when called.

We will make this:


What is a Function?

In computer science, a subroutine or subprogram (also called procedure, method, function, or routine) is a portion of code within a larger program, which performs a specific task and is relatively independent of the remaining code. Wikipedia

Why do we have functions?

A function is a way for programmers to reuse code without having to rewrite the code.

This is time saving, and often makes kode more readable, if the function names are well selected, that is.

How do we write functions?

A function is written as this in C/C++ and Arduino

returntype functionName( arguments ){
  //function body
  return returntype;

For our example we will use

  • returntype = void
    • This returntype specifies that our block of code will not return any value. Calling such a function will simply execute all the code in the function body. A return statement is redundant, as a return is implied by the closing curly bracked.
  • functionName = blinkLED
    • The name describes the action the function does. Calling this function will blink the LED.
  • function body
    • This is where the code for our function is.
  • arguments = no argument, void

Our example function:

//returntype functionName( arguments ){
void blinkLED(){

  //function body
  digitalWrite(ledPin, HIGH);   // sets the LED on
  delay(1000);                  // waits for a second
  digitalWrite(ledPin, LOW);    // sets the LED off
  delay(1000);                  // waits for a second

  //return returntype;
  //implied by closing curly bracked

About arguments:

An argument consists of both a datatype and a name. For instance, one could specify a function that adds two integers like this: int add( int x, int y){ return x+y; }. For our example the argument is non-existant, but the compiler will see it as a void argument.

Selecting function names

The funciton name should clearly state what the function will do. If you can think of many names, you should select the least verbose name.
For instance, we could replace blinkLED with setAPinHighThenLow, but this is a longer name, and I would argue, less descriptive, although more detailed.
It is also important to make your API user friendly. Arduino has selected a lowercaseUppercase naming convention, and I think Arduino users should comply to this convention.

Selecting returntype

Any type that is legal for a variable can be used for the return type. The type void means that the function does not return any value.

I will argue that selecting the datatype with the least amount of size, bytewise, will be good practice.
This will produce faster code, and in my opinion makes coding more intuitive.

Selecting parameters

Try to keep the parameter list as short as possible, but be sure to require enough info for your function to execute correctly.


Information about this page

Part of AlphaBeta Tutorials and Resources.
Last Modified: June 05, 2009, at 04:11 PM
By: AlphaBeta