constexpr int8_t pushButtonPin = 2;
constexpr int8_t ledPin = 3;

enum ledStates : int8_t {
  ZERO_PERCENT = 0,
  TWENTY_PERCENT = 1,
  FORTY_PERCENT = 2,
  SIXTY_PERCENT = 3,
  EIGHTY_PERCENT = 4,
  HUNDRED_PERCENT = 5
};

ledStates ledStatus = ZERO_PERCENT;

enum pushButtonStates : int8_t {
  PRESSED = 0,
  RELEASED = 1
};

pushButtonStates pushButtonStatus = RELEASED;

void setup() {
  Serial.begin(9600);
  pinMode(ledPin, OUTPUT);
  pinMode(pushButtonPin, INPUT_PULLUP);
}

void loop() {
  // Typecast the value to the specific state
  pushButtonStatus = (pushButtonStates)digitalRead(pushButtonPin);
  
  switch(pushButtonStatus) {
    case PRESSED:
      ledStatus = (ledStatus + 1) % 6;
    break;

    case RELEASED:
    break;
  }

  switch(ledStatus) {
    case ZERO_PERCENT:
      analogWrite(ledPin, 0);      // 0% = 0*255/100
      Serial.println("0%");
    break;

    case TWENTY_PERCENT:
      analogWrite(ledPin, 51);    // 20% = 20*255/100
      Serial.println("20%");
    break;

    case FORTY_PERCENT:
      analogWrite(ledPin, 102);   // 40% = 40*255/100
      Serial.println("40%");
    break;

    case SIXTY_PERCENT:
      analogWrite(ledPin, 153);   // 60% = 60*255/100
      Serial.println("60%");
    break;

    case EIGHTY_PERCENT:
      analogWrite(ledPin, 204);   // 80% = 80*255/100
      Serial.println("80%");
    break;

    case HUNDRED_PERCENT:
      analogWrite(ledPin, 255);   // 100% = 100*255/100
      Serial.println("100%");
    break;

    default: 
      Serial.println("CODE SHOULD NEVER ENTER HERE");
  }
  delay(100); // delay to debounce the button
}