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
);
    // TODO: Declare internal ripple carries

    full_adder_1bit adder_1 (.a(a[0]), .b(b[0]), .cin(cin),    .sum(sum[0]), .cout(c0_out));
    full_adder_1bit adder_2 (.a(a[1]), .b(b[1]), .cin(c0_out), .sum(sum[1]), .cout(c1_out));
    full_adder_1bit adder_3 (.a(a[2]), .b(b[2]), .cin(c1_out), .sum(sum[2]), .cout(c2_out));
    full_adder_1bit adder_4 (.a(a[3]), .b(b[3]), .cin(c2_out), .sum(sum[3]), .cout(cout));

    // TODO: drive cout


endmodule