A comparator has two inputs and three output bits that say whether the first input is greater, less, or equal to the second input.

4 Bit Comparator

Block Diagram

comparator

4 Bit Comparator Verilog Code

module comparator(
  input [3:0] A, B,
  output reg A_grt_B, A_less_B, A_eq_B);
  
  always@(*) begin
    A_grt_B = 0; A_less_B = 0; A_eq_B = 0;
    if(A>B) A_grt_B = 1'b1;
    else if(A<B) A_less_B = 1'b1;
    else A_eq_B = 1'b1;
  end
endmodule

Testbench Code

module tb;
  reg [3:0] A, B;
  wire A_grt_B, A_less_B, A_eq_B;
  
  comparator comp(A, B, A_grt_B, A_less_B, A_eq_B);
  
  initial begin
    $monitor("A = %0h, B = %0h -> A_grt_B = %0b, A_less_B = %0b, A_eq_B = %0b", A, B, A_grt_B, A_less_B, A_eq_B);
    repeat(5) begin
      A=$random; B=$random; #1;
    end
  end
endmodule

Output:

A = 4, B = 1 -> A_grt_B = 1, A_less_B = 0, A_eq_B = 0
A = 9, B = 3 -> A_grt_B = 1, A_less_B = 0, A_eq_B = 0
A = d, B = d -> A_grt_B = 0, A_less_B = 0, A_eq_B = 1
A = 5, B = 2 -> A_grt_B = 1, A_less_B = 0, A_eq_B = 0
A = 1, B = d -> A_grt_B = 0, A_less_B = 1, A_eq_B = 0