According to this http://www.cplusplus.com/reference/clibrary/csignal/signal.html
SIGINT is generally used/cause by the user. How do i cause a SIG
I assume this is a Win32 app...
For a "controlled" or "safe" exit, if the app uses a message loop you can use the PostQuitMessage API from inside of it, or PostMessage outside of it. Otherwise you will need to get the thread/process ID and use the TerminateThread or TerminateProcess API, depending on if you want to kill just a thread or the entire process and all threads it has spawned. It is explained nicely by Microsoft (as with all API calls) on MSDN:
http://msdn.microsoft.com/en-us/library/aa450927.aspx