Cast class into another class or convert class to another

My question is shown in this code

I have class like that

public class MainCS
{
  public int A;
  public int B;
  public int C;
  public int D; 
}

public class Sub1
{
  public int A;
  public int B;
  public int C;
}


public void MethodA(Sub1 model)
{
  MainCS mdata = new MainCS() { A = model.A, B = model.B, C = model.C };   

  // is there a way to directly cast class Sub1 into MainCS like that    
  mdata = (MainCS) model;    
}

Use JSON serialization and deserialization:

using Newtonsoft.Json;

Class1 obj1 = new Class1();
Class2 obj2 = JsonConvert.DeserializeObject<Class2>(JsonConvert.SerializeObject(obj1));

Or:

public class Class1
{
    public static explicit operator Class2(Class1 obj)
    {
        return JsonConvert.DeserializeObject<Class2>(JsonConvert.SerializeObject(obj));
    }
}

Which then allows you to do something like

Class1 obj1 = new Class1();
Class2 obj2 = (Class2)obj1;

You have already defined the conversion, you just need to take it one step further if you would like to be able to cast. For example:

public class sub1
{
    public int a;
    public int b;
    public int c;

    public static explicit operator maincs(sub1 obj)
    {
        maincs output = new maincs() { a = obj.a, b = obj.b, c = obj.c };
        return output;
    }
}

Which then allows you to do something like

static void Main()
{
    sub1 mySub = new sub1();
    maincs myMain = (maincs)mySub;
}