Overloading unary and binary operators

Unary operators

The unary operators operate on a single operand and following are the examples of Unary operators:

• The increment (++) and decrement (--) operators.
• The unary minus (-) operator.
• The logical not (!) operator.

The unary operators operate on the object for which they were called and normally, this operator appears on the left side of the object, as in !obj, -obj, and ++obj but sometime they can be used as postfix as well like obj++ or obj--.

Following example explain how minus (-) operator can be overloaded for prefix as well as postfix usage.

#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- () {
         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;
}

When the above code is compiled and executed, it produces the following result:

F: 11 I:10
F: -5 I:11

Hope above example makes your concept clear and you can apply similar concept to overload Logical Not Operators (!).

Binary operators

The binary operators take two arguments and following are the examples of Binary operators. You use binary operators very frequently like addition (+) operator, subtraction (-) operator and division (/) operator.

Following example explains how addition (+) operator can be overloaded. Similar way, you can overload subtraction (-) and division (/) operators.

#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;
}

When the above code is compiled and executed, it produces the following result:

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