Arithmetic circuits- Ripple carry adder test bench

4 BIT RIPPLE CARRY ADDER TEST BENCH
FULL ADDER
module faa(carry,sum,a,b,c);
output carry,sum;
input a,b,c;
assign sum=a^b^c;
assign carry=(a&b)|(b&c)|(c&a);
endmodule

4 BIT RIPPLE CARRY ADDER
module ripple4bit(s,carry,a,b,cin);
output [3:0]s;
output carry;
input [3:0]a,b;
input cin;
wire c1,c2,c3;
faa f1(c1,s[0],a[0],b[0],cin);
faa f2(c2,s[1],a[1],b[1],c1);
faa f3(c3,s[2],a[2],b[2],c2);
faa f4(carry,s[3],a[3],b[3],c3);
endmodule

TEST BENCH
module rippletet4bit;
reg [3:0]a,b;
reg c;
wire [3:0]sum;
wire carry;
ripple4bit r1(sum,carry,a,b,c);
initial
begin

a=0000;b=0000;c=0;
#100 a=0001;b=0001;c=0;
#100 a=0010;b=0010;c=0;
#100 a=0100;b=0100;c=0;
#100 a=0101;b=0101;c=0;
#100 a=0110;b=0110;c=0;
#100 a=0111;b=0111;c=0;
#100 a=1000;b=1000;c=0;
#100 a=1001;b=1001;c=0;
#100 a=1010;b=1010;c=0;
#100 a=1011;b=1011;c=0;
#100 a=1100;b=1100;c=0;
#100 a=1101;b=1101;c=0;
#100 a=1110;b=1110;c=0;
#100 a=1111;b=1111;c=0;
#100 a=0000;b=0000;c=1;
#100 a=0001;b=0001;c=1;
#100 a=0010;b=0010;c=1;
#100 a=0100;b=0100;c=1;
#100 a=0101;b=0101;c=1;
#100 a=0110;b=0110;c=1;
#100 a=0111;b=0111;c=1;
#100 a=1000;b=1000;c=1;
#100 a=1001;b=1001;c=1;
#100 a=1010;b=1010;c=1;
#100 a=1011;b=1011;c=1;
#100 a=1100;b=1100;c=1;
#100 a=1101;b=1101;c=1;
#100 a=1110;b=1110;c=1;
#100 a=1111;b=1111;c=1;

end
endmodule