const int analogPin = A0;
const int ledCount = 10;

int ledPins[] = {
  3, 4, 5, 6, 7, 8, 9, 10, 11, 12
};

void setup() {
  Serial.begin(9600);

  for (int thisLed = 0; thisLed < ledCount; thisLed++) {
    pinMode(ledPins[thisLed], OUTPUT);
  }
}

void loop() {
  int sensorReading = analogRead(analogPin);
  int ledLevel = map(sensorReading, 0, 1023, 0, ledCount);

  for (int thisLed = 0; thisLed < ledCount; thisLed++) {
    if (thisLed < ledLevel) {
      digitalWrite(ledPins[thisLed], HIGH); 
    }
    else {
      digitalWrite(ledPins[thisLed], LOW);
    }
  }
}