Segmenting code into functions allows a programmer to create modular pieces of code that perform a defined task and then return to the area of code from which the function was "called". The typical case for creating a function is when one needs to perform the same action multiple times in a program.
For programmers accustomed to using BASIC, functions in Arduino provide (and extend) the utility of using subroutines (GOSUB in BASIC).
Standardizing code fragments into functions has several advantages:
There are two required functions in an Arduino sketch, setup() and loop(). Other functions must be created outside the brackets of those two functions. As an example, we will create a simple function to multiply two numbers.
To "call" our simple multiply function, we pass it parameters of the datatype that it is expecting:
Our function needs to be declared outside any other function, so "myMultiplyFunction()" can go either above or below the "loop()" function.
The entire sketch would then look like this:
This function will read a sensor five times with analogRead() and calculate the average of five readings. It then scales the data to 8 bits (0-255), and inverts it, returning the inverted result.
To call our function we just assign it to a variable.
As you can see, even if a function does not have parameters and no returns is expected "(" and ")" brackets plus ";" must be given.
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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.