Step 4: How It Works - Part III
Now that we have full adders, its time to put them together to make a calculator. To connect all of the adders together, you have to connect the carry-outs to the carry-ins in a cascading fashion. So the carry-out of the first adder connects to the carry-in of the second adder and so on.
Below shows the concept. The blocks represent the adders and the arrows are the carry-ins and carry-outs.