Arrays

What is an Array?

An array is a collection of values stored under a single name. Each value has an index (position number starting from 0).

Declaring Arrays

// Method 1: Specify size and values
int leds[4] = {3, 5, 6, 9};

// Method 2: Let compiler count
int leds[] = {3, 5, 6, 9};

// Method 3: Specify size, fill later
int readings[10];  // 10 zeros

Accessing Elements

int first = leds[0];   // 3 (first element)
int second = leds[1];  // 5
int last = leds[3];    // 9

leds[2] = 10;  // Change third element

Important: Arrays are zero-indexed. An array of 4 elements has indices 0, 1, 2, 3.

Array + Loop = Power

int leds[] = {3, 5, 6, 9};
int numLeds = 4;

// Turn all LEDs on
for (int i = 0; i < numLeds; i++) {
  pinMode(leds[i], OUTPUT);
  digitalWrite(leds[i], HIGH);
}

Common Uses

• LED pin arrays: Control multiple LEDs
• Melody arrays: Store note sequences
• Lookup tables: Digit patterns for 7-segment displays
• Sensor buffers: Average multiple readings

Common Mistakes

• Buffer overflow: Accessing index beyond array size crashes the Arduino
• Off-by-one: Remember arrays start at 0, not 1
• Forgetting size: Always track array length separately