mfc dll error or win32 dll in clr app?

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C++

MFC

VisualC++

I have an mfc dll, it was an mfc console application which I want to add the code as dll to a clr c++ aoo.
code of console :

#include <windows.h>
#include <iostream>
#include <complex>

void main()
{
    double i,c,d,f,g,e;
	HDC hdc = GetDC(GetDesktopWindow());
    DWORD ret = GetDeviceCaps(hdc, HORZSIZE);
    DWORD ret2 = GetDeviceCaps(hdc, VERTSIZE);
    std::cout << "Your screen size in inches is " << ret/25.4 << "\" x " << ret2/25.4 << "\" \n";
    ReleaseDC(GetDesktopWindow(), hdc);
	i=ret/25.4;
	c=ret2/25.4;
d=0;
f=0;
d=((i*i)+(c*c));
g=sqrt(d);
std::cout << "Your screen size in inches is " << g << "\" \n";
	getchar();
}

code of mydll.dll (mydll.cpp):

// mydll.cpp : Defines the initialization routines for the DLL.
//

#include "stdafx.h"
#include "mydll.h"
#include <windows.h>
#include <iostream>
#include <complex>
#include <math.h>

#ifdef _DEBUG
#define new DEBUG_NEW
#endif

//
//TODO: If this DLL is dynamically linked against the MFC DLLs,
//		any functions exported from this DLL which call into
//		MFC must have the AFX_MANAGE_STATE macro added at the
//		very beginning of the function.
//
//		For example:
//
//		extern "C" BOOL PASCAL EXPORT ExportedFunction()
//		{
//			AFX_MANAGE_STATE(AfxGetStaticModuleState());
//			// normal function body here
//		}
//
//		It is very important that this macro appear in each
//		function, prior to any calls into MFC.  This means that
//		it must appear as the first statement within the 
//		function, even before any object variable declarations
//		as their constructors may generate calls into the MFC
//		DLL.
//
//		Please see MFC Technical Notes 33 and 58 for additional
//		details.
//

// CmydllApp

BEGIN_MESSAGE_MAP(CmydllApp, CWinApp)
END_MESSAGE_MAP()


// CmydllApp construction

CmydllApp::CmydllApp()
{
	// TODO: add construction code here,
	// Place all significant initialization in InitInstance
}


// The one and only CmydllApp object

CmydllApp theApp;


// CmydllApp initialization

BOOL CmydllApp::InitInstance()
{
	CWinApp::InitInstance();

	return TRUE;
}


void MyWin32ClassTwo()
{

			  double i,c,d,f,g,k;
			  char l; 
			  HDC hdc = GetDC(GetDesktopWindow());
    DWORD ret = GetDeviceCaps(hdc, HORZSIZE);
    DWORD ret2 = GetDeviceCaps(hdc, VERTSIZE);
      ReleaseDC(GetDesktopWindow(), hdc);
	i=ret/25.4;
	c=ret2/25.4;
d=0;
f=0;
d=((i*i)+(c*c));
g=sqrt(d);
}

how to create dll and add to win32 form (clr) application and call the dll's g variable, do I have to create function in dll?
simple answer please I am NEW to C++.
In simple how to get the horzsize of monitor in a C++ clr forms Project.

Thank you