#define Slider A0
#define nofLEDs 4
byte LEDs[nofLEDs] = {11, 10, 9, 8};
bool states[nofLEDs];


void setIO() {
  pinMode(Slider, INPUT);
  for (int i = 0; i < nofLEDs; i++) {
    pinMode(LEDs[i], OUTPUT);
  }
}

void clearStates() {
  for (int i = 0; i < nofLEDs; i++) {
    states[i] = LOW;
  }
}

void applySlider() {
  int val = analogRead(Slider);
  for (int i = 0; i < nofLEDs; i++) {
    if (val > (1024 / nofLEDs)*i) {
      states[i] = HIGH;
    }
  }
}

void setLEDs() {
  for (int i = 0; i < nofLEDs; i++) {
    digitalWrite(LEDs[i], states[i]);
  }
}

void setup() {
  setIO();      // assigning pinModes 
}

void loop() {
  clearStates();  // start with cleared states
  applySlider();  // Apply position of slider to states
  setLEDs();      // write states to pins
}