STOP AND WAIT PROTOCOL PROGRAM IN C++

#include <conio.h>
#include <dos.h>
#include <stdio.h>
#include <stdlib.h>

#define TIMEOUT 5
#define MAX_SEQ 1
#define TOT_PACKETS 8
#define inc(k) if(k<MAX_SEQ) k++; else k=0;
typedef struct
{
 int data;
}packet;
typedef struct
{
 int kind;
 int seq;
 int ack;
 packet info;
 int err;
}frame;
frame DATA;
typedef enum{frame_arrival,err,timeout,no_event} event_type;

void from_network_layer(packet *);
void to_network_layer(packet *);
void to_physical_layer(frame *);
void from_physical_layer(frame *);
void wait_for_event_sender(event_type *);
void wait_for_event_reciever(event_type *);
void reciever();
void sender();

int i=1;         //Data to be sent by sender
char turn;      //r , s
int DISCONNECT=0;
/*__________________________________________________________________________*/
void main()
{
 clrscr();
 randomize();
 while(!DISCONNECT)
 {
   sender();
   delay(400);
   reciever();
 }
 getch();
}
/*__________________________________________________________________________*/
void sender()
{
 static int frame_to_send=0;
 static frame s;
 packet buffer;
 event_type event;
 static int flag=0;

 if(flag==0)
 {
  from_network_layer(&buffer);
  s.info = buffer;
  s.seq = frame_to_send;
  printf("SENDER :  Info = %d    Seq No = %d     ",s.info,s.seq);
  turn = 'r';
  to_physical_layer(&s);
  flag = 1;
 }
 wait_for_event_sender(&event);
 if(turn=='s')
  {
   if(event==frame_arrival)
    {
      from_network_layer(&buffer);
      inc(frame_to_send);
      s.info = buffer;
      s.seq = frame_to_send;
      printf("SENDER :  Info = %d    Seq No = %d     ",s.info,s.seq);
      turn = 'r';
      to_physical_layer(&s);
    }
   if(event==timeout)
    {
      printf("SENDER : Resending Frame             ");
      turn = 'r';
      to_physical_layer(&s);
    }
  }
}
/*__________________________________________________________________________*/
void reciever()
{
 static int frame_expected=0;
 frame r,s;
 event_type event;

 wait_for_event_reciever(&event);
 if(turn=='r')
  {
   if(event==frame_arrival)
    {
     from_physical_layer(&r);
     if(r.seq==frame_expected)
      {
       to_network_layer(&r.info);
       inc(frame_expected);
      }
     else
       printf("RECIEVER : Acknowledgement Resent\n");

     turn = 's';
     to_physical_layer(&s);
    }
   if(event==err)
    {
      printf("RECIEVER : Garbled Frame\n");
      turn = 's';     //if frame not recieved
    }                 //sender shold send it again
  }
}
/*__________________________________________________________________________*/
void from_network_layer(packet *buffer)
{
   (*buffer).data = i;
   i++;
}
/*___________________________________________________________________________*/
void to_physical_layer(frame *s)
{                     // 0 means error
 s->err = random(4);  //non zero means no error
 DATA = *s;           //probability of error = 1/4
}
/*___________________________________________________________________________*/
void to_network_layer(packet *buffer)
{
 printf("RECIEVER :Packet %d recieved , Ack Sent\n",(*buffer).data);
 if(i>TOT_PACKETS)          //if all packets recieved then disconnect
  {
   DISCONNECT = 1;
   printf("\nDISCONNECTED");
  }
}
/*___________________________________________________________________________*/
void from_physical_layer(frame *buffer)
{
 *buffer = DATA;
}
/*___________________________________________________________________________*/
void wait_for_event_sender(event_type * e)
{
 static int timer=0;

 if(turn=='s')
  {
   timer++;
   if(timer==TIMEOUT)
    {
     *e = timeout;
     printf("SENDER : Ack not recieved=> TIMEOUT\n");
     timer = 0;
     return;
    }
   if(DATA.err==0)
     *e = err;
   else
    {
     timer = 0;
     *e = frame_arrival;
    }
  }
}
/*____________________________________________________________________________*/
void wait_for_event_reciever(event_type * e)
{
 if(turn=='r')
  {
   if(DATA.err==0)
     *e = err;
   else
     *e = frame_arrival;
  }
}

/*    OUTPUT

SENDER :  Info = 1    Seq No = 0     RECIEVER :Packet 1 recieved , Ack Sent
SENDER : Ack not recieved=> TIMEOUT
SENDER : Resending Frame             RECIEVER : Acknowledgement Resent
SENDER :  Info = 2    Seq No = 1     RECIEVER :Packet 2 recieved , Ack Sent
SENDER :  Info = 3    Seq No = 0     RECIEVER :Packet 3 recieved , Ack Sent
SENDER : Ack not recieved=> TIMEOUT
SENDER : Resending Frame             RECIEVER : Acknowledgement Resent
SENDER :  Info = 4    Seq No = 1     RECIEVER :Packet 4 recieved , Ack Sent
SENDER :  Info = 5    Seq No = 0     RECIEVER :Packet 5 recieved , Ack Sent
SENDER :  Info = 6    Seq No = 1     RECIEVER :Packet 6 recieved , Ack Sent
SENDER :  Info = 7    Seq No = 0     RECIEVER :Packet 7 recieved , Ack Sent
SENDER :  Info = 8    Seq No = 1     RECIEVER : Garbled Frame
SENDER : Ack not recieved=> TIMEOUT
SENDER : Resending Frame             RECIEVER :Packet 8 recieved , Ack Sent

DISCONNECTED
*/