int led[] ={2,3,4,5,6};
void setup()
{
  int i;
  for (i=0;i<5;i++)
  {
    pinMode(led[i],OUTPUT);
  }
}
void loop()
{
  int i;
  for(i=0;i<5;i++)
  {
    digitalWrite(led[i], HIGH);
    delay(100);
    digitalWrite(led[i],LOW);
    delay(100);
  }
  for(i=5;i>0;i--)
  {
    digitalWrite(led[i],HIGH);
    delay(100);
    digitalWrite(led[i],LOW);
    delay(100);
  }
}