Functions

Functions are like recipes, they store your instructions and allow us to reuse them again and again. Here's an example of how functions are created and used in C++...

float add_and_half(int a, int b) {
  float c = (a + b) / 2.0;
  return c;
}

void setup() {
  Serial.begin(9600);
}

void loop() {
  float result = add_and_half(2, 3);
  Serial.println(result);
  delay(1000);
}

int add_and_double(int a, int b) : This defines add_and_double as a function that returns a float value. It takes two parameters; a and b, both of which are int types. The code inside the curly brackets are the content of this function; they will run whenever we call the function.

float result = add_and_half(2, 3) : In this line, we call the function add_and_half. We supply it with 2 for the first parameter and 3 for the second. The value that the add_and_half function returns will be stored in the result variable.

float c = (a + b) / 2.0 : Here we add a and b together, then divide it by 2.0. Note that we are using 2.0 and not 2. If we had used 2, the Arduino will perform an integer calculation (...you can try it and see what happens).

return c : This ends the add_and_half function, and causes it to return the value of the variable c.

Return Types and void

You can create functions that returns any types of values (eg. int, float, String). If your function does not need to return any value, you should define it as type void like this...

void prints_a_and_b(int a, int b) {
  Serial.println(a);
  Serial.println(b);
}

void setup() {
  Serial.begin(9600);
}

void loop() {
  prints_a_and_b(2, 3);
  delay(1000);
}

No Parameters

If your function does not require any parameters, you should use an empty () like this...

void prints_nothing() {
  Serial.println("nothing");
}

void setup() {
  Serial.begin(9600);
}

void loop() {
  prints_nothing();
  delay(1000);
}

Exercise 1

Write a function that takes a single int as parameter, and returns the cube (power of 3) of that number.

Exercise 2

Make an alternate version of the previous function (...use a different name), and modify it so that instead of returning the cube of the provided number, it will simply print it out.