Choosing With switch

Part of the Timing Without Delay section of Coddy's Arduino journey. Lesson 8 of 18.

When one variable can have several values and each value needs its own code, a chain of if and else if gets long. switch does the same job and reads like a list:

switch (zone) {
  case 0:
    // runs when zone is 0
    break;
  case 1:
    // runs when zone is 1
    break;
  default:
    // runs when no case matched (optional)
    break;
}

switch jumps to the case whose number matches and runs the lines below it. break leaves the switch. Forget a break and the board keeps going into the next case's lines too, which is called falling through.

Here the knob is cut into four zones. analogRead() gives 0 to 1023, and dividing by 256 gives a whole number: 0 for the bottom quarter, then 1, 2 and 3 at the top. Each zone shows its own colour on the RGB LED.

Challenge

Easy

Turn the knob into a colour picker with switch:

zone 0: red (already written)
zone 1: green
zone 2: blue
zone 3: white (all three on)

Use setColor() and end each case with break;. Press Run, turn the knob, then Check.

Try it yourself

const int redPin = 9;
const int greenPin = 10;
const int bluePin = 11;

void setup() {
  pinMode(redPin, OUTPUT);
  pinMode(greenPin, OUTPUT);
  pinMode(bluePin, OUTPUT);
}

void setColor(int red, int green, int blue) {
  digitalWrite(redPin, red);
  digitalWrite(greenPin, green);
  digitalWrite(bluePin, blue);
}

void loop() {
  int zone = analogRead(A0) / 256;   // 0, 1, 2 or 3

  switch (zone) {
    case 0:
      setColor(HIGH, LOW, LOW);   // red
      break;
    // add zones 1, 2 and 3 here
  }
}

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

All lessons in Timing Without Delay

1millis()

The millis() Clock Times in unsigned long Blink Without Delay Two LEDs, Two Speeds Blink While a Button Toggles A Light on a Timer

4Precise Timing

Measure With micros()When millis() Rolls Over Button Stopwatch

2State Machines

Remember the ModeChoosing With switchNamed States With enum Traffic Light State Machine Cycle Modes With a Button

3Interrupts

A Press the Loop Misses FALLING, RISING and CHANGE Sharing With volatile Count Presses by Interrupt

Practice on your own: Arduino playground