How to prevent variable going below zero?

[tumbleweed]

if you want your number staying between 0 and 255 ... use a BYTE, instead of a WORD

That's his problem... he DOES want to use a byte but as he adds or subtracts to the byte value it wraps and gives false operation.

The way I usually handle this sort of thing is to have a routine that does the addition or subtraction with a temp copy of the variable, and only update the variable if the operation is valid.

You don't have to detect a negative number... what you want to know is if you add X to Y will it be < Y (wrapped 255) and if you subtract X from Y will it be > Y (wrapped 0). Don't modify Y until you know the answer. You can have the routine limit the results to 255 or 0 if that's how you want it to work, or ignore the operation.

[CuriousOne]

So this "wrapping" is compiler related issue and can't be fixed, as I understand?

[CuriousOne]

Technically, I solved this problem by making I change between 5 and 260, and outputting HPWM 2,I-5,10000.

[Ioannis]

If you mean a compiler problem, no. It is not.

If you mean how binary arithmetic works, yes. That is how you count, add or subtract in binary having byte, word or other size variables. In any case that is how you do it in decimal also but do not give it much attention.

The "fix" is in the answers given already to you. SELECT CASE, test before updating for valid result, etc...

Ioannis