//文件名:CHAPTER9-13.cpp
#include <set>
#include <iostream>
#if _MSC_VER > 1020   // if VC++ version is > 4.2
   using namespace std;  // std c++ libs implemented in std
#endif
int main( )
{
   set <int> s1;
   set <int> :: size_type i;
   s1.insert( 1 );
   i = s1.size( );
   cout << "The set length is " << i << "." << endl;
   s1.insert( 2 );
   i = s1.size( );
   cout << "The set length is now " << i << "." << endl;
}