I want to synchronize the parent and child process to alternatively print 1 to 10 into a file. And output which process printed the number. The following code prints alternatively, but the same number. Please help me out!

```
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <unistd.h>

#define MSGSIZE 16
int parent= 1;
int n=-1;
main ()
{
  int i;
  char *msg = "How are you?";
  char inbuff[MSGSIZE];
  int p=0;
  FILE *fp1,*fp2;
  pid_t ret;

  ret = fork ();
  if (ret > 0)
    {
      i = 0;
      while (i < 10)
    {

      n++;
     // sprintf(msg, "%d", n);
     // fp=fopen("abc.txt","a");
     // write (p[1], itoa(n,msg,MSGSIZE), MSGSIZE);
     // sleep (2);
    // fclose(fp);
      //read (p[0], inbuff, MSGSIZE);

    fp1=fopen("abc.txt","r");
    fscanf(fp1,"%d",&n);
    fclose(fp1);
    fp1=fopen("abc.txt","w");
     fprintf(fp1,"%d",n); 
    printf("Parent: %d\n", n);
      i++;
    fclose(fp1);
    sleep(2);

    }
    exit(1);
    }
  else
    {
      i = 0;
      while (i < 10)
    {

      n++;
      //sleep (1);
     // read (p[0], inbuff, MSGSIZE);

     fp2=fopen("abc.txt","r");
     fscanf(fp2,"%d",&n);
     fclose(fp2);
     fp2=fopen("abc.txt","w");

     fprintf(fp2,"%d",n);        
      printf("Child: %d\n", n);
           i++;

     sleep(2);

    }
    }
  exit (0);
}

```