69. Binary Subtractor

How do you plan to solve it?

/*Write your code here*/
module sub4_2c(
   input [3:0]a,b,
   output [3:0]diff,
   output bout);
   
   wire [4:0] cout={1'b0,a}+{1'b0,~b}+ 5'b00001;
   assign diff=cout[3:0];
   assign bout=~cout[4];
endmodule