// This example lights up 8 leds in sequence.
// The sequence direction is determined by a switch.

int p = 0;                    // holds which led is on
int s = 8;                    // digital i/o pin with switch


void setup() {  
  for (int i=0; i<8; i++) {   // set digital pins 0-7 as outputs 
    pinMode(i, OUTPUT);  
  }
  pinMode(s, INPUT);          // set digital pin 8 as input
}


void loop() {
  if (digitalRead(s) == LOW) { // read status of the switch
    p++;                       // advance p to next pin
  } else {
    p--;                       // set p to previous pin
  }

  p = (p+8) % 8;               // limit p between 0-7
  
  for (int i=0; i<8; i++) {
    if (i == p) {              // set pin p HIGH
      digitalWrite(i, HIGH);
    } else {
      digitalWrite(i, LOW);    // and all other pins LOW
    }
  }
  delay(200);                  // wait 200 millisecs
}