Adding to unsigned and signed binary integers

Question

I was wondering if someone can explain to me what happens when we add binary numbers.

Say we have 4 bits, 0b1111 and we add 1 to 0b1111. I think the binary encoding should be 0b10000; however, since there are only 4 bits the bits will change to 0b0000.

I was wondering why this happens, is it because there's not enough space? How would we add 1 to it if 0b1111 was a signed integer?

this is cause overflow, You cant show the number 8 with 3 bits/4 bit sign — Alon
– Alon, Commented May 27, 2016 at 5:38
This question may need a chapter to elaborate. If you want to know the ins and outs, check Unsigned and Signed Integers for more explanation. — anonymous
– anonymous, Commented May 30, 2017 at 2:24

Rishikesh Raje · Accepted Answer · 2016-05-27 06:04:12Z

1

if 0b1111 is an unsigned 4 bit value, with 4 bit storage, it has a value of 15. Adding 1 to it, will give you 16, which cannot be stored in 4 bits. The bits roll over and 0b0000 is stored, giving you a result of 0.

Now, if 0b1111 is a signed 4 bit value, with 4 bit storage. it is generally stored in the two's complement representation. It has a range of -8 to +7. 0b1111 will give you -1. (See here on how to convert.) Adding one to that gives you 0.

answered May 27, 2016 at 6:04

Rishikesh Raje

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