BCD_ADDER with param k = 3, array inst.

module bcd_adder #(parameter k = 3)
  (
  input [4*k - 1:0] x, y,
  input ci,
  output [4*k - 1:0] z,
  output co
  );

  wire [k-1:0] cip, cop;

  bcd_add tadd[k - 1:0](
  .x(x),
  .y(y),
  .ci(cip),
  .z(z),
  .co(cop)
  );

  assign cip[0] = ci;

  assign cip[k-1:1] = cop[k-2:0];
  assign co = cop[k-1];

endmodule


module bcd_adder_tb
  (
  output reg [11:0] x, y,
  output reg ci,
  output [11:0] z,
  output co
  );

  bcd_adder #(.k(3))
  test
  (
  .x(x),
  .y(y),
  .ci(ci),
  .z(z),
  .co(co)
  );

  integer i, j, ct = 0;

initial begin
  for(i = 0; i < 4096; i = i+1)
    if(ct == 10)
      begin
        i = i+5;
        ct = 0;
      end
    else
      begin
        #100 ct = ct + 1;
        $display("i = %h",i);
      end
  end
endmodule