# Theory for 3-bit full adder and calculations with un-/signed integers

With the following scheme, I built myself a 3-bit full adder. What I'm wondering is, and I couldn't figure this out myself, does the adder calculate with signed or unsigned values?

• Is the range for the 3-bit adder between (-4) and 3, or is it between 0 and 7?

• Alternatively, is it whatever. As in, can I choose whether I want the binary number 111 to represent (-1) or if I want it to represent 7?

The adder of course can make both addition and subtraction. The scheme I took came from here. The site has a scheme with overflow and subtraction/addition added to the scheme.

The site claims: "When is the result negative? When its most-significant bit is 1. " But I'm still not sure if that must be the ABSOLUTE truth. I'm thinking the range (-4) and 3 is necessary to calculate with subtraction. Am I correct?

Answer to my problem. The main reason we use 2s complement is in fact the advantage that we can display unsigned and signed integers on the same circuitry.

• By the wa.y, you should self-answer your question by posting a separate answer. Answers don’t belong in questions. And yes, it’s fine and encouraged to self-answer if you find a solution yourself. Commented Nov 8, 2022 at 22:50