Functions

ProgrammingBeginner25 minWrite robot functions ↓Before this: Variables and data

What you’ll learn

How to write your own functions
Parameters (inputs) and return values (outputs)
How functions make robot code readable

Functions

A function is a named block of code you can run whenever you want. You’ve already used some: digitalWrite(), delay(), setup(), loop().

void beep() {
  tone(8, 1000, 100);
}

void means it doesn’t give anything back. Call it with beep();.

Parameters

Inputs that change what the function does:

void blink(int pin, int times) {
  for (int i = 0; i < times; i++) {
    digitalWrite(pin, HIGH); delay(200);
    digitalWrite(pin, LOW);  delay(200);
  }
}
blink(13, 3);

Return values

A function can calculate something and give it back:

float toCm(long microseconds) {
  return microseconds * 0.0343 / 2;
}
float d = toCm(1160);   // 19.9

Why bother?

Readable: forward(); turnLeft(); reads like the plan.
No repeated code: fix a bug once, in one place.
Testable: check each function on its own.

Example: robot moves as functions (simulator)

function forward() { motors(50, 50); }
function turnLeft() { motors(-40, 40); }
function stop() { motors(0, 0); }

function loop() {
  if (distance() < 25) turnLeft();
  else forward();
}

Example: a function that decides

bool pathClear() {
  return readCm(3, 2) > 25;
}

void loop() {
  if (pathClear()) forward();
  else turnLeft();
}

Try it

Functions

Arena

Your code (JavaScript)

Robot commands

motors(left, right): wheel power, −100 to 100
lineLeft(), lineRight(): true over the black line
distance(): cm to the nearest thing ahead (max 200)
distanceLeft(), distanceRight(): cm to the sides
linePosition(): where the line is, −1 (left) to 1 (right), or null
millis(): milliseconds since Run
print(value): show a message below
setup() runs once; loop() runs 50 times a second

Add a reverseEasy

Write backward(speed) and use it when something is closer than 10 cm. function backward(s) { motors(-s, -s); } and in loop(): if (distance() < 10) backward(40); else if (distance() < 25) spin(); else forward(60);

A helper that returnsMedium

Write isBlocked() that returns true when anything is within 25 cm in front, and use it in loop(). function isBlocked() { return distance() < 25; } then if (isBlocked()) spin(); else forward(60);

Smart turn functionHard

Write turnToOpenSide() that spins towards whichever side has more space.

Show an answer

function turnToOpenSide() {
  if (distanceLeft() > distanceRight()) motors(-40, 40);
  else motors(40, -40);
}

Quick check

1. What does void mean before a function name?It returns nothingIt is emptyIt runs foreverIt is broken

2. In blink(13, 3), what are 13 and 3?Return valuesArguments passed to parametersVariables typesComments

3. Which keyword sends a value back from a function?sendreturnoutputgive

Finished this lesson?