CSE2050 Exam #2 11/7/02, Open books, open notes.  Name ___________________

1.  Complete the class Complex, below, by adding the three member
functions required by the "rule of 3" (40 pts).

  class Complex {
  private:
    double* z;  // z[0] is the real part, z[1] is the imaginary part
  public:
    double real() const {return z[0];}
    double imag() const {return z[1];}
    Complex(double r=0, double i=0): z(new double[2]) {
      z[0]=r;
      z[1]=i;
    }

ANSWER

    ~Complex() {delete [] z;}

    Complex(const Complex& c): z(new double[2]) {
      // or z = new double[2];
      z[0] = c.real();  // or c.z[0] or *c.z
      z[1] = c.imag();  // or c.z[1]
    }

    Complex& operator = (const Complex& c) {
      // No need for delete, new, because z is the same size.
      // Thus, no need to check for assignment to self.
      z[0] = c.real();  // or c.z[0] or *c.z
      z[1] = c.imag();  // or c.z[1]
      return *this;
    }
  };



2.  A RealNumber is a Complex whose imaginary part is always 0.  Derive
RealNumber from Complex, consistent with the example below (30 pts).

  RealNumber a, b=3;                            // a defaults to 0
  cout << a.real() << ' ' << a.imag() << endl;  // 0 0
  cout << b.real() << ' ' << b.imag() << endl;  // 3 0
  Complex c=b;
  cout << c.real() << ' ' << c.imag() << endl;  // 3 0

ANSWER

  class RealNumber: public Complex {
  public:
    RealNumber(double r=0): Complex(r, 0) {}  // or : Complex(r) {}
      // Do NOT initialize z, it is private and initialized by Complex
  };

  // No need to write the destructor, copy consructor, or operator= again
  // because the default calls these for the base class as required.
  // Writing them is incorrect because z is private.



3.  Write an abstract base class (interface) for Complex called
ComplexBase, e.g. (30 pts).

  ostream& operator << (ostream& out, const ComplexBase& c) {
    return out << c.real() << "+" << c.imag() << "i";
  }

  int main() {
    cout << Complex(3,4) << endl;       // 3+4i
    cout << RealNumber(6) << endl;      // 6+0i
    ComplexBase* p = new RealNumber(7);
    cout << *p << endl;                 // 7+0i
    delete p;                           // Calls the right destructor
    ComplexBase x;                      // Error: abstract
    return 0;
  }

ANSWER

  (We assume   class Complex: public ComplexBase {...};  )

  class ComplexBase {
  public:
    virtual double real() const = 0;
    virtual double imag() const = 0;
    virtual ~ComplexBase() {}

  // Optional protected constructor, may be omitted
  protected:
    ComplexBase() {}
  };