Unit A - Foundations

06. Loops, Arrays & Functions

Remove repetition and organise reusable code.

Estimated time 4 hours

Learning outcomes

Use for and while loops safely
Store related values in arrays
Create functions with parameters and return values
Avoid array bounds and infinite-loop faults

Parts and preparation

Arduino Uno, four LEDs, four 330 ohm resistors and breadboard.

Before power: inspect wiring, confirm supply voltage and ensure all connected circuits share GND.

Loops, Arrays & Functions instructional connection diagram — Open the diagram for a larger view. Trace every connection before building.

for loops

A for loop has initialisation, condition and update. It suits known repetitions. Ensure the condition eventually becomes false.

while loops

A while loop repeats while its condition is true. It can block the rest of a program if the condition never changes.

Arrays

An array stores same-type values under one name. Indexing starts at zero. For four items, valid indices are 0-3.

Functions

A function names a task. Parameters provide inputs; a return type describes the result. void means no value is returned. Functions improve testing and reuse.

Wiring and safe build sequence

D2, D3, D4, D5 -> separate 330 ohm resistors -> LED anodes
All LED cathodes -> GND

Power rule: switch off before moving wires. Arduino I/O pins are control signals; high-current loads require a driver and suitable external supply.

Worked sketch

Download .ino sketch

const byte leds[] = {2, 3, 4, 5};
const byte ledCount = sizeof(leds) / sizeof(leds[0]);

void setAll(bool state) {
  for (byte i = 0; i < ledCount; i++) {
    digitalWrite(leds[i], state);
  }
}

void setup() {
  for (byte i = 0; i < ledCount; i++) {
    pinMode(leds[i], OUTPUT);
  }
}

void loop() {
  for (byte i = 0; i < ledCount; i++) {
    digitalWrite(leds[i], HIGH);
    delay(150);
    digitalWrite(leds[i], LOW);
  }
  setAll(HIGH);
  delay(300);
  setAll(LOW);
}

How the code works

sizeof expression calculates the array length instead of duplicating the number 4.
setAll receives one Boolean parameter and controls every LED.

Test and record evidence

Expected result: Four LEDs chase in order, then all flash together.

Practical evidence checklist

Labelled wiring or block diagram Uploaded sketch and observed result At least one measured/tested value Fault or improvement recorded in logbook

Common faults and checks

An i <= ledCount condition is wrong because it accesses one item past the array.
Check each LED/resistor branch separately.

Extension challenge: Write a function chase(bool forward) that can run the pattern in either direction.

Check your understanding

Q1. What is the first array index?

Show answer

Q2. Why create a function?

Show answer

To name, reuse and independently test a task.