YouTip

You can redefine or overload most of the built-in operators available in C#. Thus, a programmer can use operators with user-defined types as well. Overloaded operators are special functions with the name operator followed by the symbol of the operator being defined. Like other functions, an overloaded operator has a return type and a parameter list.

For example, look at the following function:

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;
}

The above function implements the addition operator (+) for the user-defined Box class. It adds the properties of two Box objects and returns the resulting Box object.

The following program demonstrates the complete implementation:

Example

using System;

namespace OperatorOvlApplication
{
    class Box
    {
        private double length; // Length
        private double breadth; // Breadth
        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;
        }

        // Overload the + operator to add two Box objects.
        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(); // Declare Box1 of type Box
            Box Box2 = new Box(); // Declare Box2 of type Box
            Box Box3 = new Box(); // Declare Box3 of type Box
            double volume = 0.0; // Volume

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

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

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

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

            // Add two objects
            Box3 = Box1 + Box2;

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

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

The following table describes the ability to overload operators in C#:

Operator	Description
+, -, !, ~, ++, --	These unary operators take one operand and can be overloaded.
+, -, *, /, %	These binary operators take two operands and can be overloaded.
==, !=, , =	These comparison operators can be overloaded.
&&, ||	These conditional logical operators cannot be directly overloaded.
+=, -=, *=, /=, %=	These assignment operators cannot be overloaded.
=, ., ?:, ->, new, is, sizeof, typeof	These operators cannot be overloaded.

In light of the above discussion, let us extend the above example to overload more operators:

Example

using System;

namespace OperatorOvlApplication
{
    class Box
    {
        private double length; // Length
        private double breadth; // Breadth
        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;
        }

        // Overload the + operator to add two Box objects.
        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 (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 =(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(); // Declare Box1 of type Box
            Box Box2 = new Box(); // Declare Box2 of type Box
            Box Box3 = new Box(); // Declare Box3 of type Box
            Box Box4 = new Box();
            double volume = 0.0; // Volume

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

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

            // Displaying the boxes using the overloaded ToString()
            Console.WriteLine("Box1 : {0}", Box1.ToString());
            Console.WriteLine("Box2 : {0}", Box2.ToString());

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

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

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

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

            // Comparing the boxes
            if (Box1 > Box2)
                Console.WriteLine("Box1 is greater than Box2");
            else
                Console.WriteLine("Box1 is not greater than Box2");

            if (Box1 = Box2)
                Console.WriteLine("Box1 is greater than or equal to Box2");
            else
                Console.WriteLine("Box1 is not greater than or equal to Box2");

            if (Box1 <= Box2)
                Console.WriteLine("Box1 is less than or equal to Box2");
            else
                Console.WriteLine("Box1 is not less than or equal to Box2");

            if (Box1 != Box2)
                Console.WriteLine("Box1 is not equal to Box2");
            else
                Console.WriteLine("Box1 is equal to Box2");

            Box4 = Box3;
            if (Box3 == Box4)
                Console.WriteLine("Box3 is equal to Box4");
            else
                Console.WriteLine("Box3 is not equal to Box4");

            Console.ReadKey();
        }
    }
}

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

Box1 : (6, 7, 5)
Box2 : (12, 13, 10)
Volume of Box1 : 210
Volume of Box2 : 1560
Box3 : (18, 20, 15)
Volume of Box3 : 5400
Box1 is not greater than Box2
Box1 is less than Box2
Box1 is not greater than or equal to Box2
Box1 is less than or equal to Box2
Box1 is not equal to Box2
Box3 is equal to Box4