[Phillip] wanted to play with the C preprocessor. He decided to do that by creating a 4 bit full adder. We know this is pretty useless in everyday life, but it was a great learning experience.

An elementary electronic circuit in the arithmetic logic unit (ALU) of the CPU that adds one bit to another. The output of the half-adder is a result of 0 or 1 and a carry of 0 or 1. Additional ...