65. Ripple Carry Adder

How do you plan to solve it?

// 1-bit Full Adder (to be used by the 4-bit RCA)
module full_adder_1bit (
    input  a, b, cin,
    output sum, cout
);
    assign {cout, sum} = a + b + cin;

endmodule

// 4-bit Ripple Carry Adder – chain 4 full adders
module rca4_chain (
    input  [3:0] a,
    input  [3:0] b,
    input        cin,
    output [3:0] sum,
    output       cout
);
    wire c1, c2, c3;

    full_adder_1bit u_a0 (
        .a(a[0]),
        .b(b[0]),
        .cin(cin),
        .sum(sum[0]),
        .cout(c1)
    );

    full_adder_1bit u_a1 (
        .a(a[1]),
        .b(b[1]),
        .cin(c1),
        .sum(sum[1]),
        .cout(c2)
    );

    full_adder_1bit u_a2 (
        .a(a[2]),
        .b(b[2]),
        .cin(c2),
        .sum(sum[2]),
        .cout(c3)
    );

    full_adder_1bit u_a3 (
        .a(a[3]),
        .b(b[3]),
        .cin(c3),
        .sum(sum[3]),
        .cout(cout)
    );

endmodule