Parent send N numbers to child and child return back the prime numbers

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
int main(){
   int pid,a,n,p[2],p2[2],i,j,buffr1[100],buffr2[100],flag,n2=0;
a = pipe(p);
   if(a == -1)
   {
       fprintf(stderr, "Pipe Failed.\n");
       return EXIT_FAILURE;
    }
   a=pipe(p2);
   if(a == -1)
    {
       fprintf(stderr, "Pipe Failed.\n");
       return EXIT_FAILURE;
    }
    pid = fork();
   switch(pid){
       case -1:perror("main: fork");
          exit(1);
       case 0: n=read(p[0],buffr2,sizeof(buffr2));
          printf("In child process (ID: %d)\n", pid);
          n=n/sizeof(int);
          for(i=0;i<n;i++){
             flag=0;
             if(buffr2[i]<=1)
                flag=1;
             for(j=2;j<=buffr2[i]/2;j++){
                if((buffr2[i]%j)==0)
                {
                   flag=1;
                   break;
                }
             }
             if(flag==0){
                buffr1[n2]=buffr2[i];
                n2++;
             }
          }
          write(p2[1],buffr1,n2*sizeof(int));
          exit(1);
          break;
       default: printf("In parent process (ID: %d)\n", pid);
          printf("Enter the limit:- ");
          scanf("%d",&n);
          for(i=0;i<n;i++){
             printf("Enter the element %d:- ",i+1);
             scanf("%d",&buffr1[i]);
          }
          write(p[1],buffr1,n*sizeof(int));
          waitpid(pid,NULL,0);
          printf("In parent process (ID: %d)\n", pid);
          n2=read(p2[0],buffr2,sizeof(buffr2));
          n2=n2/sizeof(int);
          for(i=0;i<n2;i++)
             printf("Prime Number %d:- %d\n",i+1,buffr2[i]);
          break;
       }
      close(p[0]);
       close(p[1]);
      return 0;
}