Intending to perform nafil salaah or to keep nafil fast

In the one instance, one makes intention to keep a nafil fast or to perform a nafil salaat. But then, at the appropriate time, one changes one’s mind and does not keep the fast or perform the nafil salaat. In the second instance, one had already commenced performing nafil salaat but when one’s wudhu broke, one did not renew one’s wudhu and abandoned performing the nafil salaat. In the first instance, is it now mandatory to fast and perform the nafil salaat one had intended to perform? And, in the second instance, does performing the abandoned nafil salaat also become mandatory?