Structural full adder

module full_addr (A, B, Cin, S, Cout);

input A, B, Cin;

output S, Cout;

assign {Cout, S} = A + B + Cin;

endmodule

module adder4 (A, B, Cin, S, Cout);

input [3:0] A, B;

input Cin;

output [3:0] S;

output Cout;

wire C1, C2, C3;

full_addr fa0 (A[0], B[0], Cin, S[0], C1);

full_addr fa1 (A[1], B[1], C1, S[1], C2);

full_addr fa2 (A[2], B[2], C2, S[2], C3);

full_addr fa3 (A[3], B[3], C3, S[3], Cout);

endmodule