C :: UDP Application Simulate Packet Loss

have udp server-client application written in C. On the client side packet loss is detected using recvfrom function and sequence numbers of packets. How can I now simulate dropped packet's on the client side, for example if server is sending 1000 packet I want to drop 20% of them? I want to do this in the code, not for example using ip tables or WANEM or something like that. And one more thing, I have few clients and I want that they can dropped different packets, not the same one.

Code:
while(1){
nbytes = recvfrom(socket, buffer, MAX_SIZE, 0, (struct sockaddr *) &srv_addr, &addrlen);
if (nbytes != -1) {
// packet is received

}else{
//packet is not received
}
}