#include <iostream>
#include <map>

// for the sqrt() function, which returns a double
#include <cmath>

using namespace std;

int main()
{
  // the map is also called a "hash" in other languages
  //   (such as Perl)
  map< int, double > sqrts;
  map< int, double >::iterator i;

  while ( true )
  {
    cout << "Enter an int and I'll tell you the sqrt: ";
    int n;
    cin >> n;

    i = sqrts.find( n );   // is n already a key in the map?

         // sqrts.end() is a "placeholder" BEYOND the
         //   last element in the map (or list, vector, etc.)
    if ( i == sqrts.end() )  // not found
    {
      cout << "Oooo! That's new. I'll add it to the map.\n";
      sqrts[n] = sqrt( (double)n );
      i = sqrts.find( n );
    }
    else
    {
      cout << "I already know that one.\n";
    }

    cout << "sqrt of " << n << " is " << i->second << '\n';
  }

  return 0;
}