const int analogPin = 34;   // the pin that the potentiometer is attached to
const int ledCount = 10;    // the number of LEDs in the bar graph

int ledPins[] = 
{
  13, 15, 2, 4, 5, 18, 19, 21, 22, 23
};   // an array of pin numbers to which LEDs are attached


void setup() 
{
  // loop over the pin array and set them all to output:
  for (int thisLed = 0; thisLed < ledCount; thisLed++) 
  {
    pinMode(ledPins[thisLed], OUTPUT);
  }
}

void loop() 
{
  // read the potentiometer:
  int sensorReading = analogRead(analogPin);
  // map the result to a range from 0 to the number of LEDs:
  int ledLevel = map(sensorReading, 0, 1023, 0, ledCount);

  // loop over the LED array:
  for (int thisLed = 0; thisLed < ledCount; thisLed++) 
  {
    // if the array element's index is less than ledLevel,
    // turn the pin for this element on:
    if (thisLed < ledLevel) 
    {
      digitalWrite(ledPins[thisLed], HIGH);
    }
    // turn off all pins higher than the ledLevel:
    else 
    {
      digitalWrite(ledPins[thisLed], LOW);
    }
  }
}