C++输入/输出运算符重载

#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;
      }
      friend ostream &operator<<( ostream &output, const Distance &D ) { 
         output << F :  << D.feet <<  I :  << D.inches;
         return output;            
      }

      friend istream &operator>>( istream  &input, Distance &D ) { 
         input >> D.feet >> D.inches;
         return input;            
      }
};

int main() {
   Distance D1(11, 10), D2(5, 11), D3;

   cout << Enter the value of object :  << endl;
   cin >> D3;
   cout << First Distance :  << D1 << endl;
   cout << Second Distance : << D2 << endl;
   cout << Third Distance : << D3 << endl;

   return 0;
}