The half adder
The half adder can produce the result of adding two bits.
The half adder takes two inputs and produces two outputs. The first is the sum produced by putting the inputs through and XOR gate and the second the carry bit produced by putting the inputs through an AND gate.
The half adder has no way to feed the carry bit in from a previous calculation and so we need a more complex circuit.
Concatenating adders
By joining adders together in sequence you can build a circuit for adding n bits where n is the number of adders you connect together.
For the first calculation C is 0, for all others it is the value output as the carry bit from the previous calculation.
