C++ set lower_bound()

#include <iostream>
#include <set>
#include <string>
using namespace std;
int main()//from  w  w w .jav  a2 s . c  om
{                          // set of string objects
    set<string, less<string> > organic;
    // iterator to set
    set<string, less<string> >::iterator iter;
    organic.insert("C");  // insert organic compounds
    organic.insert("X");
    organic.insert("C");
    organic.insert("M");
    organic.insert("C");
    organic.insert("P");
    organic.insert("A");
    organic.insert("I");
    organic.insert("C");
    organic.insert("P");
    organic.insert("C");
    iter = organic.begin();    // display set
    while( iter != organic.end() )
       cout << *iter++ << '\n';
    string lower, upper;       // display entries in range
    cout << "\nEnter range (example C Czz): ";
    cin >> lower >> upper;
    iter = organic.lower_bound(lower);
    while( iter != organic.upper_bound(upper) )
       cout << *iter++ << '\n';
    return 0;
}