int led[8]={4,5,6,7,8,9,10,11};

void setup() {
  for(int i=0; i<=7; i++){
     pinMode(led[i],OUTPUT);  
  }
}
void loop() {
  for(int i=0; i<=7; i++){
    digitalWrite(led[i],HIGH);
    delay(100);
    digitalWrite(led[i],LOW);
    delay(100);
  }
for(int i=6; i>=1; i--){
  digitalWrite(led[i],HIGH);
  delay(100);
  digitalWrite(led[i],LOW);
  delay(100);
  }
}