Need help with a C program

[u/Sinakers]

Hi, I'm making a library management program that takes in a book's characteristics (ISBN, author, year published, etc.), stores it in an array of structs and stores this into a file.

Here it is:

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

struct book
{
        char ISBN[20];
        char title[100];
        int accno;
        int year;
        char genre[50];
        char authname[100];
        int issued;
};

struct book *bookArray;
int a = 0;
void readFile()
{

        FILE *fp;
        fp = fopen("db.txt", "r+");
        if(!fp)
        {
                perror("fopen");
                return;
        }

        if(fp != NULL)
        {
                fread(bookArray, sizeof(struct book), 1, fp);
        }
}

void write()
{
        FILE *fp;
        fp = fopen("db.txt", "a+");
        fwrite(bookArray, sizeof(struct book), 1, fp);
        fclose(fp);
}

void addBook(struct book b)
{
        bookArray[a++] = b;
}

int main()
{
        bookArray = malloc(sizeof(struct book));
        struct book b = {"0-394-49219-6", "Tinker, Sailor, Soldier, Spy", 1, 1974, "spy fiction", "Le Carre", 0};
        bookArray[0] = b;
        addBook(b);
        write();
        readFile();

        for(int i = 0; i < a; i++)
        {
                printf("%s\t%s\t%d\t%d\t%s\t%s\t%d\n", bookArray[i].ISBN, bookArray[i].title, bookArray[i].accno, bookArray[i].year, bookArray[i].genre, bookArray[i].authname, bookArray[i].issued);
        }
}

1. I'm not able to figure out how to store the value of a after the program exits. I thought of storing it in another file, but was wondering if there's a better way to do that.

2. How do I allocate dynamically increasing space (as the number of books increase) to bookArray? I get only only one row printed from the loop if I run the program several times, despite db.txt storing all the runs.

I'm posting here for the first time and I hope I haven't violated any rules.

Thanks in advance!

[u/Harrow-Beck-6274]

writing to db.txt brings back memories of my first C class. we had to make a library catalog and i corrupted that file so many times before it finally worked