#include <iostream>
#include <algorithm>
#include <string>
#include <set>
using std::cout;
using std::endl;
 
 
class Sort_By_Length
{
   public:
      enum sort_mode {ascending, descending};
 
      //constructor for sorting criterion
      //-default criterion uses value descending
      Sort_By_Length(sort_mode m=descending): mode(m) { }
 
      //comparison of the elements
      bool operator() (const string& s1, const string& s2) const
      {
         return  (mode == descending ? s1.length() > s2.length() : s2.length() > s2.length());
      }
 
      //comparison of the sorting criterion
      bool operator== (const Sort_By_Length& sbl)
      {
         return mode == sbl.mode;
      }
 
 
   private:
      sort_mode mode;
};
 
 
 
typedef set<string, Sort_By_Length> String_Set;
void fill_set(String_Set& set);
 
int main()
{
   //create, fill, and print set with normal element order
   //-uses default sorting criterion
   String_Set coll;
   fill_set(coll);
 
   copy(coll.begin(), coll.end(), //range
        ostream_iterator<string>(cout, "\n")); //destination
   cout << endl;
}
 
void fill_set(String_Set& set)
{
   set.insert("reallylarge");
   set.insert("small");
   set.insert("medium");
}

#include <algorithm>
#include <iostream>
#include <string>
#include <vector>
 
using namespace std;
 
struct length {
  bool operator() ( const string& a, const string& b )
  {
    return a.size() < b.size();
  }
};
 
int main()
{
  string init[] = {
    "This","is","a","test","and","aaaaa"
  };
  vector<string> v ( init, init + 6 );
 
  sort ( v.begin(), v.end(), length() );
 
  cout<< v.back() <<'\n';
}

#include <algorithm>
#include <iostream>
#include <string>
#include <vector>
 
using namespace std;
 
struct length {
  bool operator() ( const string& a, const string& b )
  {
    return a.size() < b.size();
  }
};
 
int main()
{
  string init[] = {
    "This","is","a","test","and","aaaaa"
  };
  vector<string> v ( init, init + 6 );
 
  cout<< *max_element ( v.begin(), v.end(), length() ) <<'\n';
}