/*
  set the delay times
*/

int delayTime1 = 250;
int delayTime2 = 100;

/*
  setup a flag to keep track of which delay time to use
  if flag = 1 use delayTime1
  if flag = 2 use dealyTime2
*/
int delayTimerFlag = 1;

/*
  i to keep track of which LED should be high at a given time
  i goes from 1 to 4. once it goes to 5 it is reset at 1.
  in every loop() call i is increased by 1
*/
int i = 1;

/*
  setup() function is called once when the Arduino board is powered up or reset
*/
void setup() {

  /*
    using for loop to set pin modes (from 2 to <9)
  */
  for (int pin = 2; pin < 9; pin = pin + 2) {
    /*
      set pins 2, 4, 6, and 8 as output pins
    */
    pinMode(pin, OUTPUT);
  }
}

/*
  loop() function is called repeatedly after setup() function
  indefinitely as long as the Arduino is powered on
*/
void loop() {

  /*
    i==5 means that one round is complete 
    if i is 5 reset it i to 1
    and change the delay time flag
  */
  if (i == 5) {
    i = 1;

    if (delayTimerFlag == 1) {
      delayTimerFlag = 2;
    } else {
      delayTimerFlag = 1;
    }
  }

  /*
    using for loop to write pin  (from 2 to <9 i.e. 2,4,6,8)
  */
  for (int pin = 2; pin < 9; pin = pin + 2) {
    /*
      if pin == 2*i it should be HIGH else LOW
      for example when i=2 and pin =4
      pin 2 will be LOW
      pin 4 will be HIGH cause pin(4) == 2*i(2)
      pin 6 will be LOW and
      pin 8 will be LOW
    */
    if (pin == 2 * i) {
      digitalWrite(pin, HIGH);
    } else {
      digitalWrite(pin, LOW);
    }
  }


  /*
    increase  i so that next LED can be HIGH
  */
  i++;

  /*
      delay the execution based on flag
  */
  if (delayTimerFlag == 1) {
    delay(delayTime1);
  } else {
    delay(delayTime2);
  }
}