Answer:
see attached
Explanation:
As you know, a full adder produces the binary value in (carry, output) that is the the number of true input bits among the (carry in, A, B) inputs.
The annotated diagram attached shows the bit values for a 4-bit full adder/subtractor.
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Additional comment
If the numbers are considered "signed", then the top diagram will generate an "overflow" based on the difference between the carry C4 and the output O4.
