int arr[] ={10,11,12,13};

 void setup() {
  for (int c=0;c<4;c++)
pinMode(arr[c],OUTPUT);
}

void loop() {
 for (int c=0;c<4;c++) 

{
  digitalWrite(arr[c],HIGH);
  delay(1000);
  digitalWrite(arr[c],LOW);
  delay(1000);
}
}