Spring 2005 Exam #3, open book, open notes.  Name _________________________

1.  Given the following classes, what should the base class be? (It might
not be among those listed).  (5 pts each).

                                 ANSWER
a.  Real, Complex, Integer       Complex (Real x is also Complex x + 0i)
b.  Vehicle, Car, Truck          Vehicle
c.  Bird, Fish, Dog              Animal

Which of these base classes would likely be abstract? (5 pts).

  ANSWER: Animal (because it was created just to derive from).

2.  Add the destructor and two other "rule of 3" members.  (30 pts).

  class Complex: public ComplexBase {
    static list<double> data;  // alternating imag/real data for all Complex
    list<double>::iterator pr, pi;  // points to real/imaginary parts
  public:
    Complex(double r=0, double i=0) {
      data.push_front(r);
      pr=data.begin();
      data.push_front(i);
      pi=data.begin();
    }
    double real() const {return *pr;}
    double imag() const {return *pi;}

    // ANSWER
    ~Complex() {
      data.erase(pr);
      data.erase(pi);
    }

    Complex(const Complex& c) {
      data.push_front(c.real());
      pr=data.begin();
      data.push_front(c.imag());
      pi=data.begin();
    }

    Complex& operator=(const Complex& c) {
      *pr = c.real();
      *pi = c.imag();
      return *this;
    }
  };


3.  Write ComplexBase as an interface (abstract) (20 pts).

  // ANSWER
  class ComplexBase {
    virtual double real() const = 0;
    virtual double imag() const = 0;
    virtual ~ComplexBase() {}
  };


4.  Circle Y if the following statements are legal (in the order shown)
or N if not.  Assume correct answers to 2 and 3.  (3 pts each).

  ANSWERS
  Y    Complex c;
    N  ComplexBase b;
    N  Complex *cp = new ComplexBase(1,2);
  Y    ComplexBase *bp = new Complex(3);
  Y    cout << bp->real();
    N  bp.imag() = 0;
  Y    Complex operator+(const ComplexBase& a, const ComplexBase& b);
  Y    c=c+c;
    N  throw Complex;
  Y    try {} catch (const ComplexBase& be) {}