int ledPins[] = {2,3,4,5,6,7,8,9};
void setup()
{
  pinMode(ledPins[0],OUTPUT);  //ledPins[0] = 2
  pinMode(ledPins[1],OUTPUT);  //ledPins[1] = 3
  pinMode(ledPins[2],OUTPUT);  //ledPins[2] = 4
  pinMode(ledPins[3],OUTPUT);  //ledPins[3] = 5
  pinMode(ledPins[4],OUTPUT);  //ledPins[4] = 6
  pinMode(ledPins[5],OUTPUT);  //ledPins[5] = 7
  pinMode(ledPins[6],OUTPUT);  //ledPins[6] = 8
  pinMode(ledPins[7],OUTPUT);  //ledPins[7] = 9
}

void loop() {
    
  oneAfterAnother();
  oneOnAtATime(); 
  pingPong();
  marquee();
  randomLED();
}              

void oneAfterAnother()
{
  int index;
  int delayTime = 100; 
  for(index = 0; index <= 7; index = ++index)  
  {
    digitalWrite(ledPins[index], HIGH);
    delay(delayTime);                
  }                                  

  for(index = 7; index >= 0; index = --index)  
  {
    digitalWrite(ledPins[index], LOW);
    delay(delayTime);
  }               
}

void oneOnAtATime()
{
  int index;
  int delayTime = 100;
  for(index = 0; index <= 7; index = ++index)
  {
    digitalWrite(ledPins[index], HIGH);  
    delay(delayTime);                    
    digitalWrite(ledPins[index], LOW);   
  }
}

void pingPong()
{
  int index;
  int delayTime = 100;
  for(index = 0; index <= 7; index = ++index)
  {
    digitalWrite(ledPins[index], HIGH);  
    delay(delayTime);                    
    digitalWrite(ledPins[index], LOW);   
  }
  for(index = 7; index >= 0; index = --index)
  {
    digitalWrite(ledPins[index], HIGH); 
    delay(delayTime);                    
    digitalWrite(ledPins[index], LOW);   
  }
}

void marquee()
{
  int index;
  int delayTime = 200;
  for(index = 0; index <= 3; index++)
  {
    digitalWrite(ledPins[index], HIGH);    
    digitalWrite(ledPins[index+4], HIGH);  
    delay(delayTime);                      
    digitalWrite(ledPins[index], LOW);     
    digitalWrite(ledPins[index+4], LOW);   
  }
}

void randomLED()
{
  int index;
  int delayTime;

  index = random(8);
  delayTime = 100;
  digitalWrite(ledPins[index], HIGH);  
    delay(delayTime);                    
    digitalWrite(ledPins[index], LOW);  
}