32 bit adder-subtractor

I have made this circuit in a software called logisim.....

First of all We have to make 1 bit full adder using different logic gates..

Now you have to make 8 bit adder- circuit using the concept of subcircuit in logisim.Actually subcircuit is used to make circuit less complex.For eg. to make 8 bit adder circuit we will use eight 1 bit adder circuit.You will clearly understand this after looking following figure:

Now to make 32 bit adder subtractor circuit we have to again use concept of subcircuit.

Final circuit has been displayed below:

In the above circuit if you will keep input carry as 1 then it will act as subtractor circuit otherwise adder circuit(input carry-0).I have also mentioned part for detection of overflow at right most part.