module test_adder;
   reg [3:0] a, b;
   reg 	     cin;
   
   wire [3:0]sum;
   wire      cout;
   
   full_adder_4bit dut(a, b, cin, sum, cout);

   initial
     begin
	a = 4'b0000;
	b = 4'b0000;
	cin = 1'b0;
	#50;
	a = 4'b0101;
	b = 4'b1010;
	// sum = 1111, cout = 0
	#50;
	a = 4'b1111;
	b = 4'b0001;
	// sum = 0000, cout = 1
	#50;
	a = 4'b0000;
	b = 4'b1111;
	cin = 1'b1;
	// sum = 0000, cout = 1
	#50;
	a = 4'b0110;
	b = 4'b0001;
	// sum = 1000, cout = 0

     end // initial begin
     
     initial
     	$monitor($stime,, a,, b,, cin,, sum,,, cout);
endmodule // test_adder