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Functions and Scope

Functions are reusable blocks of code which are fundamental for making your sketches more maintainable and readable. Essentially, a function is a block of code which performs a specific task.

tip

You have been using functions all along! The setup() and loop() commands are functions as well.

void setup() {
  // This runs once at the beginning
}

void loop() {
  // This repeats forever
}

Using functions​

We can use functions by defining them using a specific syntax and then calling them as required.

Defining a function​

returnType functionName(parameter1Type parameter1Name, parameter2Type parameter2Name, ...) {
    // Code to be executed
    return value; // Optional, if returnType is not void
}

In the syntax above, returnType refers to the data type of the value which is to be returned by the function. If no value is to be returned, the returnType is void. For instance, we can program our own function to turn on an LED:

void turnOnLED() {
  digitalWrite(2, HIGH);
}

Calling a function​

We can then call a function using the following syntax:

functionName(argument1, argument2);

turnOnLED(); // calls the turnOnLED() function

Scope​

All the variables we create have a property known as the scope. This means that there are two different types of scopes for variables:

  • Global variables are declared outside all functions and can be used anywhere in your program
  • Local variables are delcared inside functions, and these variables can only be used within that function.

For instance, consider this sketch:

int ledPin = 13; // Global variable

void setup() {
    pinMode(ledPin, OUTPUT);
}

void loop() {
  int delayTime = 500; // Local variable
  digitalWrite(ledPin, HIGH);
  delay(delayTime);
  digitalWrite(ledPin, LOW);
  delay(delayTime);
}

Assignment​

Your Turn
  1. Create two functions:
    • dotBlink() - turns an LED on for 200ms, then off for 200ms.
    • dashBlink() - turns an LED on for 600ms, then off for 200ms.
  2. Use these functions blink out your name in Morse code using an LED. For example, if your name is John, convert each letter to Morse code using this chart and blink it out using combinations of the functions you created.

Next Steps​

This section includes links to help you dive deeper into the topics from this lesson. It's optional, so don't worry if you choose to skip it.