int ledpins[] = {6,5,4,3,2};
int numLEDs = 5;

void setup() {
  
  for (int i = 0; i < numLEDs; i++) {
    pinMode(ledpins[i], OUTPUT);
  }
}

void loop() {
 
  for (int i = 0; i < numLEDs; i++) {
    digitalWrite(ledpins[i], HIGH);  
    delay(100);                     
    digitalWrite(ledpins[i], LOW);  
  }

    for (int i =numLEDs-1 ; i >=0; i--) {
    digitalWrite(ledpins[i], HIGH);  
    delay(100);                     
    digitalWrite(ledpins[i], LOW);  
  }
}