intro to arduino: wagging a dog tail

dog.ino

#include <Servo.h>

int servoPin = 9;

int neutral   = 0;
int happy     = 1;
int scared    = 2;
int attentive = 3;

class Dog {
  Servo servo;
  int state;

public:
  Dog() {
    state = neutral;
  }

  void Attach(int pin) {
    servo.attach(pin);
  }

  void Detach() {
    servo.detach();
  }

  void Default() {
    servo.write(40);
  }

  void Happy() {
    int angle;

    for(angle = 130; angle < 180; angle++) {
      servo.write(angle);
      delay(10);
    }

    for(angle = 180; angle > 130; angle--) {
      servo.write(angle);
      delay(10);
    }
  }

  void Scared() {
    servo.write(0);
  }

  void Attentive() {
    servo.write(110);
  }
};

Dog spike;

void setup() {
  Serial.begin(9600);
  spike.Attach(servoPin);
  spike.Default();
}

void loop() {
  if (spike.state == happy) {
    spike.Happy();
  } else if (spike.state == scared) {
    spike.Scared();
  } else if (spike.state == attentive) {
    spike.Listen();
  } else {
    spike.Default();
  }
}

void serialEvent() {
  while (Serial.available()) {
    int new_state = Serial.parseInt();

    if (Serial.read() == '\n') {
      spike.state = new_state;
    }
  }
}