C++一元运算符重载

#include <iostream>

using namespace std;

class distance {
   private:
      int feet;             // 0 to infinite
      int inches;           // 0 to 12

   public:
      // required constructors
      distance() {
         feet = 0;
         inches = 0;
      }
      distance(int f, int i) {
         feet = f;
         inches = i;
      }

      // method to display distance
      void displaydistance() {
         cout << F:  << feet <<  I: << inches <<endl;
      }

      // overloaded minus (-) operator
      distance operator- () {
         feet = -feet;
         inches = -inches;
         return distance(feet, inches);
      }
};

int main() {
   distance D1(11, 10), D2(-5, 11);

   -D1;                     // apply negation
   D1.displaydistance();    // display D1

   -D2;                     // apply negation
   D2.displaydistance();    // display D2

   return 0;
}