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, 0);

    HANDLE hFileMapping = CreateFileMapping(hFile, NULL, PAGE_READONLY, 0, 0, NULL);

    LPVOID lpFileBase = MapViewOfFile(hFileMapping, FILE_MAP_READ, 0, 0, 0);    

    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);
}