title: Create class Complex number in C#
body: <p>I tried to create class Complex number in C# with two different constructor, the first constructor takes real part and imaginary part, the second constructor takes module and argument.</p>
  
  <pre><code>public class Complex
  {
      public Complex() { }
  
      private Complex(double _re, double _im)
      {
          re = _re;
          im = _im;
      }
  
      public static double Complex_FromCartesian(double _re, double _im)
      {
          return new Complex(_re, _im);
      }
  
      public static double Complex_FromPolar(double _mod, double _arg)
      {
          var _re = _mod * Math.Cos(_arg);
          var _im = _mod * Math.Sin(_arg);
          return new Complex(_re, _im);
      }
  
      public static Complex operator +(Complex num1, Complex num2)
      {
          return new Complex(num1.re + num2.re, num2.im + num2.im);
      }
  
      public static Complex operator -(Complex num1, Complex num2)
      {
          return new Complex(num1.re - num2.re, num2.im - num2.im);
      }
  
      public double Re { get; set; }
      public double Im { get; set; }
  
      private double re, im;
  }
  </code></pre>
  
  <p>}</p>
  
  <p>but I got the same error in both constructors<br>
  <img src="https://i.stack.imgur.com/v5Bvj.png" alt="enter image description here"><br>
  How to fix that?</p>