/*   Eratosthenes' Sieve        */
/*   Demand driven discipline   */

/*   File Eratosthenes_demand_driven.c  */

#include <iostream.h> 

class Item { 
   protected:
      Item *source; 
   public:
      virtual int out() {} 
}; 

class Generator: public Item { 
      int value; 
   public: 
      int out() { return value++; } 
      Generator(){source = 0; value = 2; } 
}; 

class Filter: public Item { 
      int factor; 
   public: int out() { 
               int n; 
               n = source->out(); 
               while(!(n%factor)) { n = source->out(); }
               return n; 
               } 
       Filter(Item *src, int f){ source = src; factor = f; }
}; 


class Sieve :public Item{ 
   public: 
       int out() { 
           int n = source->out(); 
           source = new Filter(source, n); 
           return n;
           } 
       Sieve(Item *src){source =src;}
};

main() {
	Generator *g = new Generator();
	Sieve s(g);
	int max;
        int n;
        n = s.out();
        cout << "Input the upper bound" << '\n';
        cin >> max;
        cout << "These are the prime numbers between " << 2 << " and " << max << '\n';
	while (n<max){
           cout << n << " ";
           n = s.out();
           };
        cout << '\n';
}


/* Sample session: 

mix 35% g++ Eratosthenes_demand_driven.c
mix 36% a.out
Input the upper bound
100
These are the prime numbers between 2 and 100
2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97 
mix 37% a.out
Input the upper bound
200
These are the prime numbers between 2 and 200
2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97 101 103 107 109 113 127 131 137 139 149 151 157 163 167 173 179 181 191 193 197 199 
mix 38%

*/