运算符重载

#include <iostream>
using namespace std;
class Distance
{
   private:
      int feet;             // 0 到无穷
      int inches;           // 0 到 12
   public:
      // 所需的构造函数
      Distance(){
         feet = 0;
         inches = 0;
      }
      Distance(int f, int i){
         feet = f;
         inches = i;
      }
      // 显示距离的方法
      void displayDistance()
      {
         cout << "F: " << feet << " I:" << inches <<endl;
      }
      // 重载负运算符（ - ）
      Distance operator- ()  
      {
         feet = -feet;
         inches = -inches;
         return Distance(feet, inches);
      }
      // 重载小于运算符（ < ）
      bool operator <(const Distance& d)
      {
         if(feet < d.feet)
         {
             cout<<d.feet<<endl; 
            return true;
         }
         if(feet == d.feet && inches < d.inches)
         {
            return true;
         }
         cout<<d.feet<<" "<<d.inches<<endl;
         return false;
      }
};
int main()
{
   Distance D1(11, 10), D2(5, 11);
 
   if( D1 < D2 )// 运算符左侧为调用对象，右侧为参数被传递的对象 
   {
      cout << "D1 is less than D2 " << endl;
   }
   else
   {
      cout << "D2 is less than D1 " << endl;
   }
   return 0;
}

#include <iostream>
using namespace std;
class Box
{
   public:
      double getVolume(void)
      {
         return length * breadth * height;
      }
      void setLength( double len )
      {
          length = len;
      }
      void setBreadth( double bre )
      {
          breadth = bre;
      }
      void setHeight( double hei )
      {
          height = hei;
      }
      // 重载 + 运算符，用于把两个 Box 对象相加
      Box operator+(const Box b)
      {
         Box box;
         box.length = this->length + b.length;
         box.breadth = this->breadth + b.breadth;
         box.height = this->height + b.height;
         cout<<b.length<<" "<<b.breadth <<" "<<b.height<<endl; 
         return box;
      }
   private:
      double length;      // 长度
      double breadth;     // 宽度
      double height;      // 高度
};
// 程序的主函数
int main( )
{
   Box Box1;                // 声明 Box1，类型为 Box
   Box Box2;                // 声明 Box2，类型为 Box
   Box Box3;                // 声明 Box3，类型为 Box
   double volume = 0.0;     // 把体积存储在该变量中
   // Box1 详述
   Box1.setLength(6.0); 
   Box1.setBreadth(7.0); 
   Box1.setHeight(5.0);
   // Box2 详述
   Box2.setLength(12.0); 
   Box2.setBreadth(13.0); 
   Box2.setHeight(10.0);
   // Box1 的体积
   volume = Box1.getVolume();
   cout << "Volume of Box1 : " << volume <<endl;
   // Box2 的体积
   volume = Box2.getVolume();
   cout << "Volume of Box2 : " << volume <<endl;
   // 把两个对象相加，得到 Box3
   Box3 = Box1 + Box2;
   // Box3 的体积
   volume = Box3.getVolume();
   cout << "Volume of Box3 : " << volume <<endl;
   return 0;
}