All declarations inside a structure are by default public, while all members inside a class are private

false: arrays are more appropriate for the elements of the same type

We can define structure bit field members with Dot operators.
EXAMPLE:

#include <stdio.h>
int main()
{ Struct bit_field
  {  Int x.4; // it allocates only 4 bits to x
     Char C.6; // it allocates only 6 bits to C;
   };
return 0;
}

A unicast packet is the complete opposite: one machine is talking to only one other machine. All TCP connections are unicast, since they can only have one destination host for each source host. UDP packets are almost always unicast too, though they can be sent to the broadcast address so that they reach every single machine in some cases.
A multicast packet is from one machine to one or more. The difference between a multicast packet and a broadcast packet is that hosts receiving multicast packets can be on different LANs, and that each multicast data-stream is only transmitted between networks once, not once per machine on the remote network. Rather than each machine connecting to a video server, the multicast data is streamed per-network, and multiple machines just listen-in on the multicast data once it's on the network.