When adding 8 bit unsigned integers (type unsigned char), overflow occurs if there is a carry out of bit position 7. But the carry is simply discarded.

What is the value of the carry into the 8^th position? Answer: 2⁸ = 256.

For mathematical binary addition, overflow doesn't occur. Mathematically, there is no largest integer.

If overflow occurs addition using 8 bit unsigned integers, discarding the carry is the same as subtracting 256 from the mathematical addition result.

Examples

unsigned char x	unsigned char y	unsigned char z = x + y (mathematically)	(z <= 255)? z : z - 256
254	1	255	255
254	2	256	0 (= 256 - 256)
254	3	257	1 (= 257 - 256)