#include <list.h> // STL list container class (includes bool type)
template <class S>
class gen_bag{
// "adaptor" for S class to make a bag of floats.
// The S class must provide the following member functions
//    a constructor with an integer argument, the optional size of the bag
//    a destructor that removes all memory allocated by members of S
//    bool attach(float) that "adds" an element to S
//    float detach(void) that "removes" and returns an element from S
//    void reset(void) that "empties" S so that 0 elements are attached
// Note: attach and detach process the elements in unknown order
//       (which can be favorable to the internals of class S)
        int n; // number of elements in bag
        S *obj; // data structure containing elements
public: gen_bag(unsigned int max_size = 0) {obj = new S(max_size); n = 0;};
        ~gen_bag(void) {delete obj;}

        bool put_in(float x){bool flag = obj->attach(x);
                             if(flag){n++; return true;}
                             else return false;}
        // enters x into bag; duplicates are accepted;
        // returns true if the function was successful;
        // returns false otherwise (e.g., if the bag was full)

        float take_out(void){if(!is_empty())
                               {n--; return obj->detach();}
                             else return 0.0; // no el's in bag
                            }
        // returns an arbitrary element from the bag and
        // removes that single element

        int is_empty(void) {return n < 1; }
        void make_empty(void) {obj->reset();
                               n = 0;}
        // does not delete obj, just resets obj to empty
        friend class S;
};// end gen_bag

class array_bag{
   float* arr;// array of elements
   int p; // position of last element
   int size; // size of array
public:
   array_bag(unsigned int max_size) {p = 0; size = max_size;
                                     arr = new float[max_size];}
   ~array_bag(void){delete[] arr;}
   void reset(void){p = 0;}
   bool attach(float x) {if(p >= size) return false;
                         arr[p++] = x; return true;}
   float detach(void) {return arr[--p];}
};// end array_bag

class list_bag{
   list<float> lst;
public:
   list_bag(unsigned int max_size) {}
   void reset(void) {lst.erase(lst.begin(), lst.end()); }
   bool attach(float x){list<float>::iterator p = lst.insert(lst.end(), x);
                        if(p == lst.end()) return false;
                        else return true;}
   float detach(void){float x = *(lst.begin()); lst.erase(lst.begin());
                      return x;}
};// end list_bag

#include <iostream.h>
int main(void)
{gen_bag<array_bag> B(10);
 B.put_in(5.5); B.put_in(6.6);
 cout << B.take_out() <<" "<< B.take_out() << endl;
 B.make_empty(); B.put_in(7.7);

 gen_bag<list_bag> C(10);
 C.put_in(-5.5); C.put_in(-6.6);
 cout << C.take_out() <<" "<< C.take_out() << endl;
 C.make_empty(); C.put_in(-7.7);
}