int led_pin[] = {22,23,24,25,26,27,28,29};

void setup() {
  // put your setup code here, to run once:
   // put your main code here, to run repeatedly:
for(int i = 0; i < 8; i++)
{
  pinMode(led_pin[i], OUTPUT);
}

}

void loop() {
  // put your main code here, to run repeatedly:
for(int i = 0; i < 8; i++)
{
  digitalWrite(led_pin[i], HIGH);
  delay(200);
  digitalWrite(led_pin[i], LOW);
}
for(int i = 7; i >= 0; i--)
{
   digitalWrite(led_pin[i], HIGH);
  delay(200);
  digitalWrite(led_pin[i], LOW);
}
}