Arduino multiple analog buttons

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

void loop() {
  Serial.println(readButtons());
}

int readButtons(){
  return analogRead(A0);
}

/*
0    //2000R
145  //330R
329  //620R
505  //1000R
741  //3300R
871  //6200R
*/

enum Btns {NONE, ONE, TWO, THREE, FOUR, FIVE, SIX};
Btns readButtons();
Btns btn = NONE;
Btns lastBtn = NONE;

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

void loop() {
  btn = readButtons();
  if(lastBtn != btn){
    switch(btn){
    case ONE:
      Serial.println("First function to be executed");
      break;
     case TWO:
      Serial.println("Second function to be executed");
      break;
     case THREE:
      Serial.println("Third function to be executed");
      break;
     //.....
     default:
      break;
    }
    lastBtn = btn;
  }
}

Btns readButtons(){
  int adcKey= analogRead(A0); 
  if (adcKey> 1000) return NONE;
  else if (adcKey< 50) return ONE;
  else if (adcKey< 200) return TWO;
  else if (adcKey< 400) return THREE;
  else if (adcKey< 600) return FOUR;
  else if (adcKey< 800) return FIVE;
  else if (adcKey< 900) return SIX;
  else return NONE;
}