i=i++; //increment by one
The result of the above statement is not defined. That is, it is not necessarily "i + 1".
i = i + 1;
A note about "undefined behavior":
I removed the soic IC from board and used it on my own board. I mounted two identical SMT boards, one with a generic chinese pdip and the other with the soic removed, both chips soldered, and I used the same battery supply. The soic from digispark consumed 6 times more current than pdip, in sleep mode: 812uA vs 137uA. I suspect of fake chips. In this base, ...