const double feet_per_meter = 3.28;
// g++ - gnu c++ permits calculation in const initializer
const double meter_per_foot = 1.0 / feet_per_meter;
const double feet_per_mile = 5280.0;
const double meters_per_kilometer = 1000.0;
const double miles_per_foot = (1.0 / feet_per_mile);
const double miles_per_kilometer = (miles_per_foot * feet_per_meter * meters_per_kilometer);