Data Structure C++

#include 
#include 
#include 
using namespace std;
int main()
{
    set setObject;                                                   
    setObject.insert( "a" );                                           
    setObject.insert( "b" );                                              
    setObject.insert( "c" );                                               
    setObject.insert( "d" );                                          
    setObject.insert( "c" );                    // attempting a duplicate   
    cout << setObject.size() << endl;;                                   
    typedef set::const_iterator CI;
    for (CI iter = setObject.begin();                                        
          iter != setObject.end();
          iter++)
       cout << *iter << " "; 
     setObject.erase( "b" );                                               
     cout << setObject.size() << endl;                                   
     for ( CI iter = setObject.begin();                                       
          iter != setObject.end();
          iter++ )
     cout << *iter << " "; 
     return 0;
}