// Define the number of LEDs
const int numLEDs = 3;
int i = 0;
// Create an array to hold the LED pin numbers
int ledPins[numLEDs] = {3, 4, 5};

void setup() {
  // Set each LED pin as an output
  for ( i = 0; i < numLEDs; i++) {
    pinMode(ledPins[i], OUTPUT);
  }
}

void loop() {
  /* Turn on each LED in sequence
    for (initialization; condition; increment) {
    Code to be executed in each iteration
    }
  */

  for ( i = 0; i < numLEDs; i++) {
    digitalWrite(ledPins[i], HIGH); // Turn on the LED
    delay(500);                     // Wait for half a second
    digitalWrite(ledPins[i], LOW);  // Turn off the LED
  }
}