一元运算符需要两个参数，下面是二元运算符的例子。可以使用二元操作就像加(+)运算符，减(- )运算符和除法(/)运算符。

以下举例说明如何加(+)运算符可以被重载。类似的方式，可以试一下自己重载减( - )和除法(/)运算符。

#include <iostream>
using namespace std;
 
class Box
{
   double length;      // Length of a box
   double breadth;     // Breadth of a box
   double height;      // Height of a 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;
   }
   // Overload + operator to add two Box objects.
   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;
      return box;
   }
};
// Main function for the program
int main( )
{
   Box Box1;                // Declare Box1 of type Box
   Box Box2;                // Declare Box2 of type Box
   Box Box3;                // Declare Box3 of type Box
   double volume = 0.0;     // Store the volume of a box here
 
   // box 1 specification
   Box1.setLength(6.0); 
   Box1.setBreadth(7.0); 
   Box1.setHeight(5.0);
 
   // box 2 specification
   Box2.setLength(12.0); 
   Box2.setBreadth(13.0); 
   Box2.setHeight(10.0);
 
   // volume of box 1
   volume = Box1.getVolume();
   cout << "Volume of Box1 : " << volume <<endl;
 
   // volume of box 2
   volume = Box2.getVolume();
   cout << "Volume of Box2 : " << volume <<endl;
 
   // Add two object as follows:
   Box3 = Box1 + Box2;
 
   // volume of box 3
   volume = Box3.getVolume();
   cout << "Volume of Box3 : " << volume <<endl;
 
   return 0;
}

让我们编译和运行上面的程序，这将产生以下结果：

Volume of Box1 : 210
Volume of Box2 : 1560
Volume of Box3 : 5400