// 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
);
half_adder HA1(.a(a), .b(b), .sum(sum1), .carry(carry1));
half_adder HA2(.a(sum1), .b(cin), .sum(sum), .carry(carry2));
assign cout = carry1 + carry2;
endmodule