Convert console application to dll on Visual Studio

Go to Project Property Page/Cofniguration Properties
General/Configuration Type, change as “Dynamic Library(.dll)”
C/C++/Code Generation/Runtime Library, change as “/MDd”
C/C++/Preprocessor/Preprocessor Definitions, add macro “YOURDLL_EXPORTS”
Linker/System/SubSystem, change as “Windows(/Subsystem:windows)”
Linker/Advanced/Import Library, change as ...$(TargetName).lib
Create an header contains the export interfaces

#pragma once
#ifdef YOURDLL_EXPORTS
#define YOURDLL_API __declspec(dllexport)
#else
#define YOURDLL_API __declspec(dllimport)
#pragma comment (lib, "YOURDLL.lib")
#endif

And then add a dllmain.cpp file contains the allocation and deallocation for this dll

#include "stdafx.h"
BOOL APIENTRY DllMain( HMODULE hModule,
                       DWORD  ul_reason_for_call,
                       LPVOID lpReserved
                     )
{
    UNREFERENCED_PARAMETER(hModule);
    UNREFERENCED_PARAMETER(lpReserved);

    switch (ul_reason_for_call)
    {
    case DLL_PROCESS_ATTACH:
    case DLL_THREAD_ATTACH:
    case DLL_THREAD_DETACH:
    case DLL_PROCESS_DETACH:
        break;
    }
    return TRUE;
}

YOURDLL_API int Add(int lhs, rhs);

as the abovev code, the Add function will be explored outside to invoke. If you want to explore an entire class, you should declare a class like this way:

class YOURDLL_API CTest
{
public:
    static int Add(int lhs, rhs);
};