void setup() {
      // use a for loop to initialize each pin as an output:
            for (int thisPin = 8; thisPin <= 13; thisPin++) {
                      pinMode(thisPin, OUTPUT);
                                  }
                                              }

                                                          void loop() {
                                                                        // loop from the lowest pin to the highest:
                                                                                        for (int thisPin = 8; thisPin <= 13; thisPin++) {
                                                                                                            // turn the pin on:
                                                                                                                                    digitalWrite(thisPin, HIGH);
                                                                                                                                                                delay(100);
                                                                                                                                                                                                // turn the pin off:
                                                                                                                                                                                                                                    digitalWrite(thisPin, LOW);
                                                                                                                                                                                                                                                                          }

                                                                                                                                                                                                                                                                                                                  // loop from the highest pin to the lowest:
                                                                                                                                                                                                                                                                                                                                                            for (int thisPin = 13; thisPin >= 8; thisPin--) {
                                                                                                                                                                                                                                                                                                                                                                                                          // turn the pin on:
                                                                                                                                                                                                                                                                                                                                                                                                                                                            digitalWrite(thisPin, HIGH);
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  delay(100);
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            // turn the pin off:
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          digitalWrite(thisPin, LOW);
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          }
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          }