In terms of int type (short ushort int uint etc.), there's a lot of guessing going on. It's definitely not pure C++, but it's pretty close. If you type 0xFFFFFFFFU, then it will convert to an unsigned number. Otherwise, it converts to -1 and then back to 0xFFFF for the hex output. Notice that if you type "-1", you get the same hex result as if you type 0xFFFFFFFF.
Note: The hover over number popup code displays some numbers like this in both signed and unsigned. The calculator doesn't.
Unlike C++, for the non-bitwise operators, Slick-C auto increases the int size.
0xFFFFFFFFU+1 -- no overflow here
0xFFFFFFFFFFFFFFFFU+1 -- no overflow here either. Slick-C ints up to 32 digits.
Hope this makes sense. It's never exactly C++ 64-bit or 32-bit arithmetic. This calculator supports floating point too.