// Half Adder primitive
module half_adder (
input a, b,
output sum, carry
);
xor(sum,a,b);
and(carry,a,b);
endmodule
// Full Adder using 2 Half Adders
module full_adder_struct (
input a, b, cin,
output sum, cout
);
wire w1,w2,w3;
half_adder half(.a(a),.b(b),.sum(w1),.carry(w2));
half_adder full(.a(w1),.b(cin),.sum(sum),.carry(w3));
or(cout,w2,w3);
endmodule