015. Dynamic Array in C.c

/* Dynamic Array in C */

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

/*  * This stores the total number of books in each shelf.  */
int* total_number_of_books;

/*  * This stores the total number of pages in each book of each shelf.
    * The rows represent the shelves and the columns represent the books.   */
int** total_number_of_pages;

int main()
{
    int total_number_of_shelves;
    scanf("%d", &total_number_of_shelves);
    
    int total_number_of_queries;
    scanf("%d", &total_number_of_queries);
    
    total_number_of_books = (int *)malloc(total_number_of_shelves * sizeof(int));
    total_number_of_pages = (int **)malloc(total_number_of_shelves * sizeof(int*));

   for(int i = 0 ; i < total_number_of_shelves ; i++)
   {
       total_number_of_books[i] = 0;
       total_number_of_pages[i] = NULL;
   }
    
    while (total_number_of_queries--) {
        int type_of_query;
        scanf("%d", &type_of_query);
        
        if (type_of_query == 1) {
           
            int x, y;
            scanf("%d %d", &x, &y);

            total_number_of_books[x]++; // increament the no. of books on shelf

            if(total_number_of_books[x] == 1) // we are going to insert the very first book in the shelf 'x' so we don't need realloc right now
                total_number_of_pages[x] = malloc(sizeof(int)); 
            else
                total_number_of_pages[x] = realloc(total_number_of_pages[x], total_number_of_books[x]*sizeof(int));

            total_number_of_pages[x][total_number_of_books[x] - 1] = y;

        } else if (type_of_query == 2) {
            int x, y;
            scanf("%d %d", &x, &y);
            printf("%d\n", *(*(total_number_of_pages + x) + y));
        } else {
            int x;
            scanf("%d", &x);
            printf("%d\n", *(total_number_of_books + x));
        }
    }

    if (total_number_of_books) {
        free(total_number_of_books);
    }
    
    for (int i = 0; i < total_number_of_shelves; i++) {
        if (*(total_number_of_pages + i)) {
            free(*(total_number_of_pages + i));
        }
    }
    
    if (total_number_of_pages) {
        free(total_number_of_pages);
    }
    
    return 0;
}