ICONVERTIBLE

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

namespace ConsoleApplication

{

    public struct ComplexNumber : IConvertible

    {

        private double real;

        private double imaginary;

        public ComplexNumber(double real, double imaginary)

        {

            this.real = real;

            this.imaginary = imaginary;

        }

        public TypeCode GetTypeCode()

        {

            return TypeCode.Object;

        }

        public bool ToBoolean(IFormatProvider provider)

        {

            throw new InvalidCastException();

        }

        public byte ToByte(IFormatProvider provider)

        {

            throw new InvalidCastException();

        }

        public char ToChar(IFormatProvider provider)

        {

            throw new InvalidCastException();

        }

        public sbyte ToSByte(IFormatProvider provider)

        {

            throw new InvalidCastException();

        }

        public short ToInt16(IFormatProvider provider)

        {

            throw new InvalidCastException();

        }

        public int ToInt32(IFormatProvider provider)

        {

            throw new InvalidCastException();

        }

        public long ToInt64(IFormatProvider provider)

        {

            throw new InvalidCastException();

        }

        public ushort ToUInt16(IFormatProvider provider)

        {

            throw new InvalidCastException();

        }

        public uint ToUInt32(IFormatProvider provider)

        {

            throw new InvalidCastException();

        }

        public ulong ToUInt64(IFormatProvider provider)

        {

            throw new InvalidCastException();

        }

        public float ToSingle(IFormatProvider provider)

        {

            throw new InvalidCastException();

        }

        public double ToDouble(IFormatProvider provider)

        {

            return this.real;

        }

        public decimal ToDecimal(IFormatProvider provider)

        {

            throw new InvalidCastException();

        }

        public DateTime ToDateTime(IFormatProvider provider)

        {

            throw new InvalidCastException();

        }

        public string ToString(IFormatProvider provider)

        {

            return this.real.ToString() + (this.imaginary >= 0 ? "+" : "") + this.imaginary.ToString() + "i";

        }

        public Object ToType(Type conversionType, IFormatProvider provider)

        {

            throw new InvalidCastException();

        }

    }

    class Program

    {

        static void Main(string[] args)

        {

            ComplexNumber c = new ComplexNumber(5, -6);

            Console.WriteLine("Conversion to string: {0}", Convert.ToString(c));

            Console.WriteLine("Conversion to double: {0}", Convert.ToDouble(c));

            c = new ComplexNumber(-7, 9);

            Console.WriteLine("Conversion to string: {0}", Convert.ToString(c));

            Console.WriteLine("Conversion to double: {0}", Convert.ToDouble(c));

            Console.ReadKey();

        }

    }

}