You can redefine or overload the operators built in C ා. Therefore, programmers can also use operators of user-defined types. Overloaded operators are functions with special names defined by the keyword operator followed by the symbol of the operator. Like other functions, overloaded operators have return types and parameter lists.

For example, look at the following functions:

public static Box operator+ (Box b, Box c)
{
   Box box = new Box();
   box.length = b.length + c.length;
   box.breadth = b.breadth + c.breadth;
   box.height = b.height + c.height;
   return box;
}

Implementation of operator overloading

The following program demonstrates the complete implementation:

using System;

namespace OperatorOvlApplication
{
   class Box
   {
      private double length;      // length
      private double breadth;     // width
      private double height;      // height

      public double getVolume()
      {
         return length * breadth * height;
      }
      public void setLength( double len )
      {
         length = len;
      }

      public void setBreadth( double bre )
      {
         breadth = bre;
      }

      public void setHeight( double hei )
      {
         height = hei;
      }
      // heavy load + Operator to put two Box Object addition
      public static Box operator+ (Box b, Box c)
      {
         Box box = new Box();
         box.length = b.length + c.length;
         box.breadth = b.breadth + c.breadth;
         box.height = b.height + c.height;
         return box;
      }

   }

   class Tester
   {
      static void Main(string[] args)
      {
         Box Box1 = new Box();         // statement Box1，Type is Box
         Box Box2 = new Box();         // statement Box2，Type is Box
         Box Box3 = new Box();         // statement Box3，Type is Box
         double volume = 0.0;          // volume

         // Box1 Detailed
         Box1.setLength(6.0);
         Box1.setBreadth(7.0);
         Box1.setHeight(5.0);

         // Box2 Detailed
         Box2.setLength(12.0);
         Box2.setBreadth(13.0);
         Box2.setHeight(10.0);

         // Box1 Volume
         volume = Box1.getVolume();
         Console.WriteLine("Box1 Volume: {0}", volume);

         // Box2 Volume
         volume = Box2.getVolume();
         Console.WriteLine("Box2 Volume: {0}", volume);

         // Add two objects
         Box3 = Box1 + Box2;

         // Box3 Volume
         volume = Box3.getVolume();
         Console.WriteLine("Box3 Volume: {0}", volume);
         Console.ReadKey();
      }
   }
}

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

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

Overloadable and non overloadable operators

The following table describes the ability of operator overloading in C ා:

Example

For the above discussion, let's extend the above example to overload more operators:

using System;

namespace OperatorOvlApplication
{
    class Box
    {
        private double length;      // length
        private double breadth;     // width
        private double height;      // height

        public double getVolume()
        {
            return length * breadth * height;
        }
        public void setLength( double len )
        {
            length = len;
        }

        public void setBreadth( double bre )
        {
            breadth = bre;
        }

        public void setHeight( double hei )
        {
            height = hei;
        }
        // heavy load + Operator to put two Box Object addition
        public static Box operator+ (Box b, Box c)
        {
            Box box = new Box();
            box.length = b.length + c.length;
            box.breadth = b.breadth + c.breadth;
            box.height = b.height + c.height;
            return box;
        }

        public static bool operator == (Box lhs, Box rhs)
        {
            bool status = false;
            if (lhs.length == rhs.length && lhs.height == rhs.height
                    && lhs.breadth == rhs.breadth)
            {
                status = true;
            }
            return status;
        }
        public static bool operator !=(Box lhs, Box rhs)
        {
            bool status = false;
            if (lhs.length != rhs.length || lhs.height != rhs.height
                    || lhs.breadth != rhs.breadth)
            {
                status = true;
            }
            return status;
        }
        public static bool operator <(Box lhs, Box rhs)
        {
            bool status = false;
            if (lhs.length < rhs.length && lhs.height                < rhs.height && lhs.breadth < rhs.breadth)
            {
                status = true;
            }
            return status;
        }        public static bool operator >(Box lhs, Box rhs)
        {
            bool status = false;
            if (lhs.length > rhs.length && lhs.height
                    > rhs.height && lhs.breadth > rhs.breadth)
            {
                status = true;
            }
            return status;
        }

        public static bool operator <=(Box lhs, Box rhs)
        {
            bool status = false;
            if (lhs.length <= rhs.length && lhs.height                <= rhs.height && lhs.breadth <= rhs.breadth)
            {
                status = true;
            }
            return status;
        }        public static bool operator >=(Box lhs, Box rhs)
        {
            bool status = false;
            if (lhs.length >= rhs.length && lhs.height
                    >= rhs.height && lhs.breadth >= rhs.breadth)
            {
                status = true;
            }
            return status;
        }
        public override string ToString()
        {
            return String.Format("({0}, {1}, {2})", length, breadth, height);
        }

    }

    class Tester
    {
        static void Main(string[] args)
        {
            Box Box1 = new Box();          // statement Box1，Type is Box
            Box Box2 = new Box();          // statement Box2，Type is Box
            Box Box3 = new Box();          // statement Box3，Type is Box
            Box Box4 = new Box();
            double volume = 0.0;   // volume

            // Box1 Detailed
            Box1.setLength(6.0);
            Box1.setBreadth(7.0);
            Box1.setHeight(5.0);

            // Box2 Detailed
            Box2.setLength(12.0);
            Box2.setBreadth(13.0);
            Box2.setHeight(10.0);

            // Use overloaded ToString() Show two boxes
            Console.WriteLine("Box1:  {0}", Box1.ToString());
            Console.WriteLine("Box2:  {0}", Box2.ToString());

            // Box1 Volume
            volume = Box1.getVolume();
            Console.WriteLine("Box1 Volume: {0}", volume);

            // Box2 Volume
            volume = Box2.getVolume();
            Console.WriteLine("Box2 Volume: {0}", volume);

            // Add two objects
            Box3 = Box1 + Box2;
            Console.WriteLine("Box3:  {0}", Box3.ToString());
            // Box3 Volume
            volume = Box3.getVolume();
            Console.WriteLine("Box3 Volume: {0}", volume);

            //comparing the boxes
            if (Box1 > Box2)
                Console.WriteLine("Box1 greater than Box2");
            else
                Console.WriteLine("Box1 No more than Box2");
            if (Box1 < Box2)           Console.WriteLine("Box1 less than Box2");
            else           Console.WriteLine("Box1 Not less than Box2");
            if (Box1 >= Box2)
                Console.WriteLine("Box1 Greater than or equal to Box2");
            else
                Console.WriteLine("Box1 Not greater than or equal to Box2");
            if (Box1 <= Box2)           Console.WriteLine("Box1 Less than or equal to Box2");
            else           Console.WriteLine("Box1 Not less than or equal to Box2");
            if (Box1 != Box2)           Console.WriteLine("Box1 Not equal to Box2");
            else           Console.WriteLine("Box1 Be equal to Box2");
            Box4 = Box3;
            if (Box3 == Box4)           Console.WriteLine("Box3 Be equal to Box4");
            else           Console.WriteLine("Box3 Not equal to Box4");
            Console.ReadKey();
        }
    }
}

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

Box1:  (6, 7, 5)
Box2:  (12, 13, 10)
Box1 Volume: 210
Box2 Volume: 1560
Box3:  (18, 20, 15)
Box3 Volume: 5400
Box1 No more than Box2
Box1 less than Box2
Box1 Not greater than or equal to Box2
Box1 Less than or equal to Box2
Box1 Not equal to Box2
Box3 Be equal to Box4