Calling C++ code from C# using structs

I'm trying to learn how to call unmanaged code from C# but I'm finding it difficult. So far I have managed to set up a simple scenario using basic types that work:

Test.h:

#pragma once

class TestWCM
{
public:
    int Hello();
private:
};

Test.cpp:

#include "Test.h"


int TestWCM::Hello() 
{
    return 42;
}

I then created a Visual C++ Class Library project:

WCM_Wrapper_Lib.h:

#include "C:\Test.h"
#include "C:\Test.cpp"

using namespace System;

namespace WCM_Wrapper_Lib {

    public ref class TestWrapper
    {
    public:
        TestWrapper();
        ~TestWrapper();
        int Hello();


    private:
        TestWCM* test;
    };
}

WCM_Wrapper_Lib.cpp:

#include "stdafx.h"

#include "WCM_Wrapper_Lib.h"

WCM_Wrapper_Lib::TestWrapper::TestWrapper()
{
    test = new TestWCM();
}

WCM_Wrapper_Lib::TestWrapper::~TestWrapper()
{
    delete test;
}

int
 WCM_Wrapper_Lib::TestWrapper::Hello()
{
    return test->Hello();
}

Finally I Created a Windows Forms Application where I added the .dll as a reference.

Form1.cs:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using WCM_Wrapper_Lib;

namespace WCM2_GUI
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            TestWrapper testWrapper = new TestWrapper();

            MessageBox.Show(testWrapper.Hello().ToString());
        }
    }
}

Now my question is, how would I have to modify this code if instead of an int, I would like Hello() to return a simple struct instead:

struct TestStruct
{
    int first;
    float second;
};