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
);
    // TODO: implement 1-bit full adder (structural or dataflow)
    assign sum = a ^ b ^ cin;
    assign cout = ( a & cin) | (b & cin ) | ( a &b); 
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 c0,c1,c2,c3,c4;
    assign c0 = cin;
    // TODO: Declare internal ripple carries
    full_adder_1bit a1(.a(a[0]), .b(b[0]), .cin(c0), .sum(sum[0]) ,.cout(c1));
    full_adder_1bit a2(.a(a[1]), .b(b[1]), .cin(c1), .sum(sum[1]), .cout(c2));
    full_adder_1bit a3 (.a(a[2]), .b(b[2]), .cin(c2), .sum(sum[2]),.cout(c3));
    full_adder_1bit a4 (.a(a[3]), .b(b[3]), .cin(c3), .sum(sum[3]), .cout(c4));
    assign cout = c4;
    
    // TODO: instantiate 4 full adders and chain carries


    // TODO: drive cout


endmodule