Serial example pro Jakub Hrachovec

void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);
  Serial.println("a - ano  n - ne");
}

void loop() {
  // put your main code here, to run repeatedly:
  int x = Serial.available();
  if ( x > 0 )
  {
    char z = Serial.read();
    switch (z)
    {
      case 'a':
        Serial.println("Ano");
      break;

      case 'n':
        Serial.println("Ne");
      break;

      case 10:
        // New line
      break;

      case 13:
        // Enter
      break;

      default:
        Serial.println("Nesmysl");
    }
  }
}