CSE2050 Spring 2004 Exam #3, open book, open notes.  Name _________________

1.  Circle T for true or F for false (3 pts each).                 ANSWERS
                                                                   -------
A derived class constructor should initialize inherited data members.   F
Constructors are never virtual.                                         T
Destructors are never virtual.                                          F
A pointer to derived class may point at a base object.                  F
If a base class needs a copy constructor, then so does the derived.     F

A derived class may access inherited protected data members.            T
A class with pure virtual member functions is abstract.                 T
An abstract class defines an interface to a hierarchy of classes.       T
A reference to base class may refer to a derived object.                T
Assignment from derived to base, b=d, changes the type of b to derived. F

2.  Which of Tree, Plant, Flower, or Leaf should be a base class? (5 pts)

  ANSWER: Plant  (Flower and Tree are derived from Plant, but Leaf is not.)

3.  Write B as an interface for D.  Show all code (25 pts).

  class D: public B {
    string x;
  public:
    D(const string& a = "") {x=a;}
    string get() const {return x;}
  };

  // ANSWER
  class B {
  public:
    virtual string get() const = 0;
    virtual ~B() {}
    // optional: protected: B() {}
  };


4.  Given B and D above (assuming B is correct), circle OK if the statement
compiles or ERROR if not.  (3 pts each)

                           ANSWERS
                           -------
  B b;                     ERROR
  D d;                     OK
  cout << D("hi").get();   OK
  B &r = &d;               ERROR (no points off if wrong)
  D d = B();               ERROR

5.  A TestMap<K,V> is like a map<K,V> except that it has an extra member
function, test(k), which returns true if k is a key in the TestMap (without
changing it), as in the example below.  Derive TestMap from map and show
all code (25 pts).

  TestMap<string, double> m;
  m["hi"]=3.5;
  bool a = m.test("hi");  // true
  bool b = m.test("bye"); // false
  if (a && !b) cout << m.size() << endl;  // 1

  // ANSWER
  template <class K, class V>
  class TestMap: public map<K, V> {
  public:
    bool test(const K& k) const {
      return find(k) != end();
    }
  };