a) compile-time error: cannot instantiate a
   class with a pure virtual method
b) okay
c) okay
d) okay
e) okay
f) okay
g) compile-time error, I has type I*, e has type E*, and
   E is not a subtype of I
h) okay
i) compile-time error, C not a subclass of D
j) okay, h wird zu NULL
k) okay, m wird zu d
l) okay
m) okay
n) okay)
o) compile-time error, see (g)

 =====

 template<type T, bool isend(T)>
 int read(List<T> l)
 {
   int n = 0;
   while (true)
   {
     T x;
     cin >> x ;
     if (!cin) return -1;
     if (isend(x)) return n;
     l.append(x);
     n++;
   }
 }

 template<typename T> class List
 {
   int len;
   ...

   // complexity O(n), not O(1)
   public void appendV1(T&x)
   {
     insert(len,x);
   }

   Node *head;
   Node *tail;

   List(): head(NULL), tail(NULL), len(0) { }

   // complexity O(1)
   public void appendV2(T&x)
   {
     Node<T> *node = new Node<T>(x,NULL);
     if (tail == NULL)
       head = node;
     else
       tail->next = node;
     tail = node;
     len++;
   }
 }

 =====

 template<class T>
 class ArrayQueue: public BoundedQueue<T>
 {
   T* a;
   int l;
   int n;
   int h;
   int t;
 public:
   ArrayQueue(int s):
     a(new T[s]), l(s), n(0), h(0), t(0)
   { }
   ~ArrayQueue()
   {
     delete a[];
   }
   bool isempty() { return n == 0; }
   bool isfull() { return n == l; }
   void put(T& x)
   {
     // if (isfull()) resize();
     a[t] = x;
     t = (t+1)%l;
     n++;
   }
   T get()
   {
     T x = a[h];
     h = (h+1)%l;
     n--;
     return x;
   }
 private:
   void resize()
   {
     int n0 = 2*n;
     T* a0 = new T[n0];
     for (int i = 0; i < n-h; i++)
       a0[i] = a[h+i];
     for (int i = n-h; i < n; i++)
       a0[i] = a[i-(n-h)];
     delete[] a;
     a = a0; h = 0; t = n; l = n0;
   }
 };

 ==================

 set<string> getArticleIds(Shop* s)
 {
   set<string> result;
   list<Article*> as = s->articles();
   for (list<Article*>::iterator it = as.begin();
        it != as.end(); it++)
   {
     Article* a = *it;
     string id = a->getId();
     result.insert(id);
   }
   return result;
 }

 ==================

 class Work
 {
   int t;
   int r;
 public:
   Work(int t0, int r0 = 0):
     t(t0), r(r0),
   { }
   // copy constructor automatically generated
   Work(const Work& w):
     t(w.t), r(w.r)
   { }
   void add(int t0)
   {
     t += t0;
   }
   void printSalary()
   {
     int s = t*r;
     cout << (s/100) + "," + (s%100);
   }
   bool subtract(int t0)
   {
     if (t < t0) return false;
     t -= t0;
     return true;
   }
   static void reset(Work& w)
   {
     w.t = 0;
   }
   int compare(const Work& v)
   {
     int s = t*r;
     int s0 = v.t*v.r;
     if (s == s0) return 0;
     if (s < s0) return 1;
     return -1;
   }
};