I am using DevC++ and I am trying to write a dll. I am using the following code but I get this error.

Code:
C:Dev-Cppc++ dll string$Makefile.win [Build Error]  No rule to make target `C++_DLL_STRINGprivate.rc', needed by `C++_DLL_STRINGprivate.res'.  Stop.
dllmain.cpp
Code:
/* Replace "dll.h" with the name of your header */
#include "dll.h"
#include <windows.h>

DLLEXPORT string returnstring(void);

BOOL APIENTRY DllMain (HINSTANCE hInst     /* Library instance handle. */ ,
                       DWORD reason        /* Reason this function is being called. */ ,
                       LPVOID reserved     /* Not used. */ )
{
    switch (reason)
    {
      case DLL_PROCESS_ATTACH:
        break;

      case DLL_PROCESS_DETACH:
        break;

      case DLL_THREAD_ATTACH:
        break;

      case DLL_THREAD_DETACH:
        break;
    }

    /* Returns TRUE on success, FALSE on failure */
    return TRUE;
}
dll.h
Code:
#include <cstdlib>
#include <iostream>
#ifndef _DLL_H_
#define _DLL_H_

#if BUILDING_DLL
# define DLLEXPORT __declspec (dllexport)
#else /* Not BUILDING_DLL */
# define DLLIMPORT __declspec (dllimport)
#endif /* Not BUILDING_DLL */
using namespace std;

DLLEXPORT string returnstring(void)
           {
 string my_string("hello big world");
           return my_string;
           }



#endif /* _DLL_H_ */
untitled1.rs(needed for program I am using the dll with)
Code:
#include "dll.h"
STRINGTABLE
BEGIN
{
     1 "returnstring%[s%returnstring%"
}

Why do I get this error and how do I fix it.