Introducing variables on the Arduino.

variables.ino

// Turn two LEDs on then off.

// Declare variables for later use.
int greenLED;
int redLED;

void setup () {
  // Assign values to our variables.
  greenLED = 2;
  redLED = 4;
  // Set the LEDs as outputs.
  pinMode(greenLED, OUTPUT);
  pinMode(redLED, OUTPUT);
}

void loop () {
  // Turn the LEDs on.
  digitalWrite(greenLED, HIGH);
  digitalWrite(redLED, HIGH);
  // Relax, take some time.
  delay(1000);
  // Turn the LEDs off.
  digitalWrite(greenLED, LOW);
  digitalWrite(redLEDa, LOW);
  delay(1000);
}