// This shows how to use a function name, that is already in the std namespace
#include <iostream>
#include <cmath>
using namespace std;
// Class for pairs of numbers
class TwoDouble{
public:
  double x,y;
}; 
namespace mynames{ // protect function name from conflict with std namespace
  double distance(const TwoDouble &, const TwoDouble &) ;
}
int main()
{
  TwoDouble point1,point2;
  point1.x = 1.0;  
  point1.y = 2.0;   point2.x = -2.0;    point2.y = 1.0;
  cout<<"distance="<<mynames::distance(point1,point2)<<endl;
  return 0;
}
namespace mynames{
  // distance between two points (x,y)
  double distance(const TwoDouble  & c1, const TwoDouble & c2) {
    return ( sqrt(pow(c1.x-c2.x,2) + pow(c1.y-c2.y,2) ) );
  }
}