How to tell if a file is an EXE or a DLL?

How to tell if a file is an EXE or a DLL?

 void DumpFile(LPWSTR filename)
 {
     HANDLE hFile = CreateFile(filename, GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, );

     HANDLE hFileMapping = CreateFileMapping(hFile, NULL, PAGE_READONLY, , , NULL);

     LPVOID lpFileBase = MapViewOfFile(hFileMapping, FILE_MAP_READ, , , );    

     PIMAGE_DOS_HEADER pDosHeader = (PIMAGE_DOS_HEADER)lpFileBase;

     PIMAGE_NT_HEADERS pNTHeader = (PIMAGE_NT_HEADERS)((DWORD)pDosHeader + (DWORD)pDosHeader->e_lfanew);

     if ((pNTHeader->FileHeader.Characteristics & IMAGE_FILE_DLL))
          printf("dll");
     if ((pNTHeader->FileHeader.Characteristics & IMAGE_FILE_EXECUTABLE_IMAGE))
          printf("exe");
     else
          printf("????");

     UnmapViewOfFile(lpFileBase);
     CloseHandle(hFileMapping);
     CloseHandle(hFile);
 }