int led [] = {2,3,4,5,6,7,8,9,10,11};

void setup() {
  // put your setup code here, to run once:
Serial.begin(9600);
int i;
for(i = 0; i<10; i++){
  pinMode(led[i] , OUTPUT);
}
}

void loop() {
  // put your main code here, to run repeatedly:

for(int i=0; i<10; i++){
  digitalWrite(led[i] , 1);
  delay(100);
  digitalWrite(led[i] , 0);
  delay(100);
}

for(int i=9; i>=0; i--){
digitalWrite(led[i] , 1);
delay(100);
digitalWrite(led[i] , 0);
delay(100);
}
delay(1000);
for(int i=0; i<10; i+=2){
  digitalWrite(led[i] , 1);
  delay(100);
  digitalWrite(led[i] , 0);
  delay(100);
}

for(int i=9; i>=0; i-=2){
digitalWrite(led[i] , 1);
delay(100);
digitalWrite(led[i] , 0);
delay(100);
}
delay(1000);
}