SendMessage to Main Thread

[Dimension]

Hi,

I'm using Win32 API. I'm executing a worker Thread after launching application.

 myThread = CreateThread(NULL, 0, SendStr, NULL, 0, &dw);

Now, from the Thread SendStr, I want to send Message back to Main Thread to execute something and return either TRUE or FALSE. How can I achieve that? Code example will be great. Thanks

DWORD WINAPI SendStr (LPVOID pParam)
{
      
      if (something is TRUE)
         // Send Message to Main Thread to execute something to check for the  status TRUE or FALSE

}