`timescale 1ns / 1ps

module z1top_adder (
    input [3:0] BUTTONS,
    input [1:0] SWITCHES,
    output [5:0] LEDS
);

    wire [2:0] adder_operand1, adder_operand2;
    wire [3:0] adder_result;

    // First operand:  {SWITCHES[0], BUTTONS[1], BUTTONS[0]}
    assign adder_operand1 = {SWITCHES[0], BUTTONS[1:0]};
    // Second operand: {SWITCHES[1], BUTTONS[3], BUTTONS[2]}
    assign adder_operand2 = {SWITCHES[1], BUTTONS[3:2]};
    // Result: {LEDS[3], LEDS[2], LEDS[1], LEDS[0]}
    assign LEDS[3:0] = adder_result;
    assign LEDS[5:4] = 0;

    // Module instantation of the structural_adder logic   
    structural_adder user_adder(
        .a(adder_operand1),
        .b(adder_operand2),
        .sum(adder_result)
    );

endmodule