postmessage

I am very new to MFC DLL.
class CMyMFCDllApp : public CWinApp
{
//..
};

.cpp file:
__declspec(dllexport) int __stdcall Func()
{
ComputeCalc();
return 0;
}

void CallFunc()
{
//I like to call Func using PostMessage.
}
:cool:

I don't understand your question;
Why PostMessage?
Func() is exported from the DLL, so you can call it directly an app that links to the DLL.