C++赋值运算符重载

#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;
      }
      void operator = (const Distance &D ) { 
         feet = D.feet;
         inches = D.inches;
      }

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

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

   cout << First Distance : ; 
   D1.displayDistance();
   cout << Second Distance :; 
   D2.displayDistance();

   // use assignment operator
   D1 = D2;
   cout << First Distance :; 
   D1.displayDistance();

   return 0;
}