module alutask(code,a,b,c);
input[1:0] code;
input[3:0] a,b;
output[4:0] c;
reg[4:0] c;

task my_and;
input[3:0] a,b;
output[4:0] out;
integer i;
begin
for(i=3;i>=0;i=i-1)
out[i]=a[i]&b[i];
end
endtask

always@(code or a or b)
  begin
   case(code)
   2'b00: my_and(a,b,c);
   2'b01: c=a|b;
   2'b10: c=a-b;
   2'b11: c=a+b;
   endcase
  end
endmodule