library.c

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

#define MAX 100
#define EXIT_CHOICE 10

#define USERS_FILE "users.txt"
#define BOOKS_FILE "books.txt"

struct customer {
  char fname[MAX];
  char lname[MAX];
  int id;
};

typedef struct customer customer_t;

struct book{
  char title[MAX];
  char author[MAX];
  int id;
};

typedef struct book book_t;


int user_count = 0;
int book_count = 0;

FILE *user_file, *book_file;


int get_count(FILE *input) {
  int pos = ftell(input);
  rewind(input);
  int count = fread(&count, sizeof(int), 1, input);
  fseek(input, pos, SEEK_SET);
  return count;
}

void set_count(FILE *input, int count) {
  int pos = ftell(input);
  rewind(input);
  fwrite(&count, sizeof(int), 1, input);
  fseek(input, pos, SEEK_SET);
}
int get_input () {
  int c;
  printf(
      "Choose from the following options :\n"
       "1. Display all registered users\n"
       "2. Display all books\n"
       "3. Display all borrowers\n"
       "4. Add a new user\n"
       "5. Add a new book\n"
       "6. Issue a new book\n"
       "7. Accept back a book\n"
       "8. Generate fine\n"
       "10. Exit\n\n\n"
      );
  scanf("%d", &c);
	
  int a;					// exhaust scanf's "\n" from stdin 		
  while ((a = getchar()) != EOF && a != '\n')
    continue;

  return c;
}

void display_users() {
  customer_t customers[MAX];
  int pos = ftell(user_file);
  rewind(user_file);
  fread(customers, sizeof(customer_t), user_count, user_file);
  printf("%d elements present\n", user_count);
  for (int i = 0; i < user_count; i++) {
    printf("%d\t%s\t%s\n", customers[i].id, customers[i].fname, customers[i].lname);
  }
  fseek(user_file, pos, SEEK_SET);
}

void add_user() {
  customer_t customer;
  printf("Enter name:\n");
  fgets(customer.fname, MAX, stdin);  
  if (customer.fname != NULL) {
    customer.id = user_count++;
    fwrite(&customer, sizeof(customer), 1, user_file);
  } 
  set_count(user_file, user_count);
}

void display_books(){
  book_t books[MAX];
  int pos = ftell(book_file);
  rewind(book_file);
  fread(books,sizeof(book_t), book_count, book_file);
  printf("%d elements present\n", book_count);
  for(int i = 0 ; i<book_count ; i++){
    printf("%d | %s | %s ",books[i].id,books[i].title,books[i].author);
  }
  fseek(book_file, pos, SEEK_SET);
}


void add_book(){
 book_t book;
 printf("Enter title: ");
 fgets(book.title, MAX, stdin);
 printf("Enter author: ");
 fgets(book.author, MAX, stdin);
 if(book.title != NULL){
  book.id = book_count++;
  fwrite(&book, sizeof(book), 1, book_file);
 }
}

int main () {
  int choice;
  user_file = fopen(USERS_FILE, "rwb");
  book_file = fopen(BOOKS_FILE, "rwb");
  while ((choice = get_input()) != EXIT_CHOICE) {
    switch (choice) {
      case 1: display_users();
	      break;
      case 2: display_books();
	      break;
      case 4: add_user();
	      break;
      case 5: add_book();
	      break;
      
    }
  }
  fclose(user_file);
  fclose(book_file);
  printf("Saving data..\n");
  return 0;
}