You need a thread for that
Look here: http://msdn.microsoft.com/en-us/library/y6h8hye8(v=vs.80).aspx
You are currently writing your code in the "main thread" (which usually is also your frame code).
So if you run something that takes time to complete it will halt the execution of your main thread, if you run it in a second thread your main thread will continue.
Update:
I've missed the part that you want to exit immediately.
execl() is likely what you want.
#include <unistd.h>
int main(){
execl("C:\\path\\to\\updater.exe", (const char *) 0);
return 0;
}
The suggested CreateProcess() can be used as well but execl is conforming to POSIX and would keep your code more portable (if you care at all).
#include <unistd.h>
extern char **environ;
int execl(const char *path, const char *arg, ...);
Update:
tested on Win-7 using gcc as compiler