// Half Adder primitive
module half_adder (
input a, b,
output sum, carry
);
assign sum = a ^ b;
assign 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 HA_1(.a(a), .b(b), .sum(w1), .carry(w2));
half_adder HA_2(.a(w1), .b(cin), .sum(sum), .carry(w3));
or or_1(cout,w2,w3);
endmodule