int notnine = ~nine;
If you’re worried about only the last byte:
int notnine = ~nine & 0x000000FF;
And if you’re only interested in the last nibble:
int notnine = ~nine & 0x0000000F;
The ~ operator is the bitwise negation, while the mask gives you only the byte/nibble you care about.
If you truly are interested in only the last nibble, the most simple is:
int notnine = 15 - nine;
Works for every nibble. 🙂