int datapin = 2; 
int clockpin = 3;
int latchpin = 4;
int potentiometer = A0;

byte data = 0;

void shiftWrite(int desiredPin, boolean desiredState){
  bitWrite(data,desiredPin,desiredState);

  shiftOut(datapin, clockpin, MSBFIRST, data);

  digitalWrite(latchpin, HIGH); 
  digitalWrite(latchpin, LOW); 
}

void oneAfterAnother(int level)
{
  int index;

  for(index = 0; index < level; index++)
  {
    shiftWrite(index, HIGH);
    //delay(100);   
  }

  for(index = level; index <= 7; index++)
  {
    shiftWrite(index, LOW);
  }
}

void setup() {
  pinMode(datapin, OUTPUT);
  pinMode(clockpin, OUTPUT);  
  pinMode(latchpin, OUTPUT);
  pinMode(potentiometer, INPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
  int potVal = analogRead(potentiometer);
  oneAfterAnother(potVal / 128);
}