void setup() {
  // put your setup code here, to run once:
  pinMode(A0, INPUT);
  for(int i = 2; i < 12; i++) {
    pinMode(i, OUTPUT);
  }
  Serial.begin(9600);
}

void loop() {
  // put your main code here, to run repeatedly:
  int a = analogRead(A0);
  int b = map(a, 0, 1023, 2, 11);

  for(int i = b + 1; i < 12; i++){
    digitalWrite(i, LOW);
  }

  for(int j = b; j > -1; j--){
    digitalWrite(j, HIGH);
  }
  delay(100);
}