use of pointer

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
struct Books
{
    char title[100];
    char author[100];
    char subject[100];
    int Id;
};
int main()
{
    struct Books *ptr;
    int i,n;
    printf("Enter The Numbers Of Books : ");
    scanf("%d",&n);
    fflush(stdin);
    printf("\ndetails of %d c programming books:\n",n);
    ptr=(struct Books*) malloc(n * sizeof(struct Books));
    for ( i = 0; i < n; i++)
    {
        printf("enter the book %d title:",i+1);
        gets((ptr+i)->title);
        printf("enter the book %d author:",i+1);
        gets((ptr+i)->author);
        printf("enter the book %d subject:",i+1);
        gets((ptr+i)->subject);
        printf("enter the book %d id: ",i+1);
        scanf("%d",&(ptr+i)->Id);
        fflush(stdin);
        printf("\n");
    }
    for ( i = 0; i < n; i++)
    {
        printf("\nbook %d title : %s\n",i+1,(ptr+i)->title);
        printf("book %d author : %s\n",i+1,(ptr+i)->author);
        printf("book %d subject : %s\n",i+1,(ptr+i)->subject);
        printf("book %d Id : %d\n\n",i+1,(ptr+i)->Id);
    }
    return 0;
}