Как мне избавиться от исключения stackoverflowexception

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Поле никогда не используется не знаю почему? -- & gt; private int realValue и private int imaginaryValue

Что я уже пробовал:

using System;

class Complex
    { 

    public class ComplexNum
{
    private int realValue;
    private int imaginaryValue;

}

   public Complex(int realPart, int imaginaryPart)
        {
           this.realValue = realPart;
            this.imaginaryValue = imaginaryPart;
        
        }

    public Complex()
    {
        this.realValue = 0;
       this. imaginaryValue = 0;
}

        public int realValue
        {
            get
                { return realValue; }
            set
                { realValue = value; }

        }

        public int imaginaryValue
        {
            get
               { return imaginaryValue; }
            set
                { imaginaryValue = value; }
         }

        public override string ToString()
        {
    return string.Format(" ({0}, {1})", realValue, imaginaryValue);

            }

    public void add(Complex a, Complex b)
{
    this.realValue = a.realValue + b.realValue;
    this.imaginaryValue = a.imaginaryValue + b.imaginaryValue;

}
    public void subtract(Complex a, Complex b)
{
    this.realValue = a.realValue + b.realValue;
    this.imaginaryValue = a.imaginaryValue + b.imaginaryValue;
        Console.WriteLine("Press enter to exit.");
        Console.ReadLine();
}
   
    }

    public class ComplexTest
        {
            
    public static void Main(string[] args)
    {
        Console.WriteLine("Complex Numbers\n");

        Complex a = new Complex(6, 8);
        Complex b = new Complex(10, 18);

        Complex result1 = new Complex();
        Complex result2 = new Complex();

        Console.WriteLine("1st Number:");
        Console.WriteLine(a.ToString());
        Console.WriteLine("2nd Number:");
        Console.WriteLine(b.ToString());

        result1.add(a, b);
        Console.Write("\nTest Addition:\nAfter Adding:");
        Console.WriteLine(result1.ToString());
        Console.ReadLine();


        result2.subtract(a, b);

        Console.Write("\nTest Subtraction:\nAfter Subtracting: ");
        Console.WriteLine(result2.ToString());
        Console.ReadLine();

        Console.WriteLine("Press enter to exit.");
        Console.ReadLine();




    }
}

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