You "just" obtain a handle (HPROCESS) to the process and call TerminateProcess() on it.
The catch it that you're got be able to obtain PROCESS_TERMINATE access right to handle, which usually means you have to be an administrator, and then you have to explicity grant yourself SeDebugPrivilege privilege.
Andy
PS Technically, you're not using C++ to stop the process; you're calling a WIN32 API function (which is C) using C++.