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 sum = a^b^cin;
    assign cout = a&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 [2:0]w_cout;

    full_adder_1bit ff1(a[0],b[0],cin,sum[0],w_cout[0]);
    full_adder_1bit ff2(a[1],b[1],w_cout[0],sum[1],w_cout[1]);
    full_adder_1bit ff3(a[2],b[2],w_cout[1],sum[2],w_cout[2]);
    full_adder_1bit ff4(a[3],b[3],w_cout[2],sum[3],cout);
endmodule