Quiz

const int btnA = 8;
const int btnB = 9;
const int btnC = 10;

int answer = -1;

void setup(){
  pinMode(btnA, INPUT);
  pinMode(btnB, INPUT);
  pinMode(btnC, INPUT);
  Serial.begin(9600);
}

void loop(){
  waitForStart();
  answer = getAnswer();
  if(answer > -1)
    Serial.print(answer);
  delay(100);
}

void waitForStart(){
  while(true){
    if(Serial.available() > 0)
      if(Serial.read() == '3')
        return;
    delay(100);
  }
  return;
}

char getAnswer(){
  while(true){
    if(digitalRead(btnA) == HIGH)
      return '0';
    else if(digitalRead(btnB) == HIGH)
      return '1';
    else if(digitalRead(btnC) == HIGH)
      return '2';
    delay(100);
  }
}