module half_add3(a,b,sum,cout);
input a,b;
output sum,cout;
reg sum,cout;

always @(a or b)
begin
case ({a,b})               		//真值表描述
2'b00: begin  sum=0; cout=0;  end
2'b01: begin  sum=1; cout=0;  end
2'b10: begin  sum=1; cout=0;  end
2'b11: begin  sum=0; cout=1;  end
endcase
end
endmodule