Enhanced ComplexNumber class Learn programming C#

using System;
class ComplexNumber
{
    protected double a, b;

    public ComplexNumber(double realPart, double imaginaryPart)
    {
        a = realPart;
        b = imaginaryPart;
    }


    public double GetReal()
    {
        return a;
    }


    public void SetReal(double a)
    {
        this.a = a;
    }


    public double GetImaginary()
    {
        return b;
    }


    public void SetImaginary(double b)
    {
        this.b = b;
    }


    public new string ToString()
    {
        return "(" + a + "," + b + ")";
    }


    public double GetMagnitude()
    {
        return Math.Sqrt((a * a) + (b * b));
    }


    public void Add(ComplexNumber c2)
    {
        a += c2.GetReal();
        b += c2.GetImaginary();
    }

}

class ComplexTest
{
    static void Main()
    {
        ComplexNumber number = new ComplexNumber(5, 2);
        Console.WriteLine("Number is: " + number.ToString());

        number.SetImaginary(-3);
        Console.WriteLine("Number is: " + number.ToString());

        Console.Write("Magnitude is: ");
        Console.WriteLine(number.GetMagnitude());

        ComplexNumber number2 = new ComplexNumber(-1, 1);
        number.Add(number2);
        Console.Write("After adding: ");
        Console.WriteLine(number.ToString());
    }
}