Verilog code to implement a D flip-flop circuit.

Here's an example Verilog code to implement a D flip-flop circuit:

module dflipflop(
input D,
input CLK,
output Q,
output Q_bar
);

reg Q_next;

always @(posedge CLK) begin
Q <= Q_next; Q_bar <=

Q_next;
  end
  
  always @(D) begin
    Q_next <= D;
  end
  
endmodule

In this Verilog code, the `dflipflop` module takes one input `D`, one clock input `CLK`, and outputs two signals `Q` and `Q_bar`. The `Q` output is the output of the flip-flop, and `Q_bar` is the complement of `Q`.

The `always` block triggered by the clock edge updates the output `Q` and `Q_bar` based on the value of `Q_next`, which is updated by the `always` block triggered by changes in input `D`.

Whenever there is a positive edge on the `CLK` input, the `always` block is triggered to update the output `Q` and `Q_bar` to the value of `Q_next`. The `always` block triggered by changes in `D` updates the value of `Q_next` to the value of `D`.

Note that in this implementation, the output signals `Q` and `Q_bar` are declared as combinational logic, which means that they are updated based on the value of `Q_next` in response to a clock edge. Also, `Q_next` is declared as a `reg` type since it is updated in an `always` block.

This is just one example implementation of a D flip-flop circuit in Verilog. There are many other ways to implement a flip-flop, depending on the specific requirements of the design.