C++ Class Inheritance Constructors in derived class

#include <iostream>
using namespace std;
class Counter/*from ww  w.  j  a va  2s .c  om*/
{
   protected:                            //NOTE: not private
   unsigned int count;                //count
   public:
   Counter() : count(0)               //constructor, no args
   {  }
   Counter(int c) : count(c)          //constructor, one arg
   {  }
   unsigned int get_count() const     //return count
   { return count; }
   Counter operator ++ ()             //incr count (prefix)
   { return Counter(++count); }
};
class CountDn : public Counter
{
   public:
   CountDn() : Counter()              //constructor, no args
   { }
   CountDn(int c) : Counter(c)        //constructor, 1 arg
   { }
   CountDn operator -- ()             //decr count (prefix)
   { return CountDn(--count); }
};
int main()
{
   CountDn c1;                           //class CountDn
   CountDn c2(100);
   cout << "\nc1=" << c1.get_count();
   cout << "\nc2=" << c2.get_count();
   ++c1; ++c1; ++c1;                     //increment c1
   cout << "\nc1=" << c1.get_count();
   --c2; --c2;                           //decrement c2
   cout << "\nc2=" << c2.get_count();
   CountDn c3 = --c2;                    //create c3 from c2
   cout << "\nc3=" << c3.get_count();
   cout << endl;
   return 0;
}