module 1bit_add_sub (Cout, Sum, A, B, Cin, Inv);
   
   // Fill in your code below here

endmodule // 1bit_add_sub


module 8bit_add_sub(COUT, SUM, A, B, CIN, INV);
        
   // Fill in your code below here

endmodule // 8bit_add_sub

        
module stimulus;

   // Fill in the definitions of inputs and outputs
   // and the test values for the adder-subtractor circuit here.

endmodule // stimulus