69. Binary Subtractor

How do you plan to solve it?

/*Write your code here*/
module sub4_2c (
    input [3:0] a,
    input [3:0] b,
    output  [3:0] diff,
    output  bout 
);
       wire cout;

       assign {bout, diff} = a + (~b) + 4'b0001;
       //assign bout = ~cout;

endmodule