Basics 
AddersAn adder performs addition of two bits. The half adder has two inputs  A and B  and two outputs, the sum S and carry C. The output of a half adder is the sum of two onebit numbers, with C being the most significant of these two outputs. A full adder has three inputs  A, B, and a carry in Cin  and two outputs  the sum S and carry Cout  such that multiple adders can be used to add larger numbers.
These two components are made of standard gates:
