8 i/p (1bit wide) ADDER:-

module add8 (cout3,cout2,cout1,s,a,b,c,d,e,f,g,h);
input a,b,c,d,e,f,g,h;
output cout3,cout2,cout1,s;
add7 ad1 (c2,c1,s1,a,b,c,d,e,f,g);
ha h1 (c3,s,s1,h);
ha h2 (c4,cout1,c3,c1);
ha h3 (cout3,cout2,c4,c2);
endmodule

Testbench :-

module adtb ();
reg a,b,c,d,e,f,g,h;
wire cout2,cout1,s;
add8 dut (cout3,cout2,cout1,s,a,b,c,d,e,f,g,h);
integer j;
initial
begin
for (j=0;j<=255;j=j+1)
begin
{a,b,c,d,e,f,g,h}= j;
#1;
$display(a,b,c,d,e,f,g,h,":",cout3,cout2,cout1,s);
end
end
endmodule