- Exercises

#include <iostream>
#include <ostream>
namespace Distance{
  class MyDistance{
    public:
      MyDistance(double i):m(i){}
      friend MyDistance operator +(const MyDistance& a, const MyDistance& b){
        return MyDistance(a.m + b.m);
      }
      friend MyDistance operator -(const MyDistance& a, const MyDistance& b){
        return MyDistance(a.m - b.m);
      }
      friend std::ostream& operator<< (std::ostream &out, const MyDistance& myDist){
        out << myDist.m << " m";
         return out;
      }
    private:
      double m;
  };
  namespace Unit{
    MyDistance operator "" _km(long double d){
      return MyDistance(1000*d);
    }
    MyDistance operator "" _m(long double m){
      return MyDistance(m);
    }
    MyDistance operator "" _dm(long double d){
      return MyDistance(d/10);
    }
    MyDistance operator "" _cm(long double c){
      return MyDistance(c/100);
    }
  }
}
using namespace Distance::Unit;
int main(){
  std:: cout << std::endl;
  std::cout << "1.0_km: " << 1.0_km << std::endl;
  std::cout << "1.0_m: " << 1.0_m << std::endl;
  std::cout << "1.0_dm: " << 1.0_dm << std::endl;
  std::cout << "1.0_cm: " << 1.0_cm << std::endl;
  std::cout << std::endl;
  std::cout << "1.0_km + 2.0_dm +  3.0_dm - 4.0_cm: " << 1.0_km + 2.0_dm +  3.0_dm - 4.0_cm << std::endl;
  std::cout << std::endl;
}