int led_pin = 3;
int pot_pin = A0;

int led_val, pot_val, ser_val;
int pot_old_val, ser_old_val;
bool lastComponent = false;
// false -> Serial monitor
// true -> potentiometer

void setup() {
  pinMode(led_pin, OUTPUT);

  Serial.begin(9600);
  Serial.println();
}

void loop() {
  readPotentiometer();
  readSerialMonitor();

  // we have to find the last component
  if (pot_val != pot_old_val) {
    lastComponent = true;
  }
  if (ser_val != ser_old_val) {
    lastComponent = false;
  }

  // choose component
  if(lastComponent == true) {
    led_val = pot_val;
  }
  else {
    led_val = ser_val;
  }

  analogWrite(led_pin, led_val);
  printInfo();

  // update old values
  pot_old_val = pot_val;
  ser_old_val = ser_val;
}

void printInfo() {
  Serial.print("Pot: ");
  Serial.print(pot_val);
  Serial.print("\tSer: ");
  Serial.print(ser_val);
  Serial.print("\tLed: ");
  Serial.println(led_val);
}

void readSerialMonitor() {
  if (Serial.available() > 0) {
    ser_val = Serial.parseInt();
    Serial.read();
  }
}

void readPotentiometer() {
  pot_val = analogRead(pot_pin)/4;
}