Sort an array based on variable upon insertion - c

Question

I have been writing a small program for a library database of book structures. An array is malloc allocated and initialized with 0's in each indexes ibsn long variable and a menu is prompted allowing choices. Upon adding a book it is placed into the first available position in the array (first position where the ISBN number is !=0).
My question is how can I add a book to the array whereby it places it sorted by the isbn number first checking if there is space in array?
Example: Book with ISBN 1234 entered into array; Second book added with ISBN 123 and is placed at first index moving the previous book to the next index.
void addbook(book_t* lib, int size)
{
int i;
//// Loop through the array until you find an empty element
for (i = 0; i < size; i++) {
/// Found an empty element
if ((lib + i)->isbn == 0) {
//// Ask for and store the book details
printf("Please enter the book name\n");
scanf("%s", (lib + i)->name);
printf("Please enter the book author\n");
scanf("%s", (lib + i)->author);
printf("Please enter the book number\n");
scanf("%ld", &(lib + i)->isbn);
printf("Please enter the book price\n");
scanf("%lf", &(lib + i)->price);
printf("We will now ask you for the release date of the book by day then month then year");
printf("\nPlease enter release date for this book (dd):"); //user able to change default
scanf("%d", &(lib + i)->releaseDate.date);
printf("\nPlease enter release month for this book (mm):"); //user able to change default
scanf("%d", &(lib + i)->releaseDate.month);
printf("\nPlease enter release year for this book (yyyy):"); //user able to change default
scanf("%d", &(lib + i)->releaseDate.year);
printf("\nDate entered is (%d / %d / %d)", (lib + i)->releaseDate.date, (lib + i)->releaseDate.month, (lib + i)->releaseDate.year); //user able to change default
/// Set i to size so that the loop finished
i = size;
}
//// If no empty element found and at the last element of the array
/// then library is not found
else if (i == size - 1)
{
printf("The array is full\n");
}
}
}
I have employed a similar method when deleting a book whereby if the book searched is found it is moved to the last space in the array and has its variables set to 0.
void deleteBook(book_t *lib, int size) {
int i, j, location = 0;
long searchISBN;
int found = 0;
printf("Enter ISBN to search\n");
scanf("%ld", &searchISBN);
for (i = 0; i < size; i++) {
if ((lib + i)->isbn == searchISBN) {
found++;
printf("Book Name %s\n", (lib + i)->name);
printf("Book Author %s\n", (lib + i)->author);
printf("Book ISBN %ld\n", (lib + i)->isbn);
printf("Book Price %lf\n", (lib + i)->price);
location = i;
i = size;
} else
if (i == size - 1) {
location++;
}//add to location and try again
}
if (found == 1) {
for (j = location; j < size; j++) {
strcpy(lib->name, (lib + j)->name);
strcpy(lib->author, (lib + j)->author);
(lib)->isbn = (lib + j)->isbn;
(lib)->price = (lib + j)->price; //user able to change default
(lib)->releaseDate.date = (lib + j)->releaseDate.date;
(lib)->releaseDate.month = (lib + j)->releaseDate.month;
(lib)->releaseDate.year = (lib + j)->releaseDate.year;
}//end swapping of elements
strcpy(lib->name, "0");
strcpy(lib->author, "0");
(lib)->isbn = 0;
(lib)->price = 0;
(lib)->releaseDate.date = 0;
(lib)->releaseDate.month = 0;
(lib)->releaseDate.year = 0;
} else {
printf("not found");
}
}//end deleteBook method

Answer 1

Your function deleteBook does not work correctly: it copies the fields of all entries after the found one over the first entry in the array. You should just copy the remaining entries as a block with memmove(). Use memmove() as opposed to memcpy() because the source and destination memory areas overlap.
Here is a corrected version:
#include <stdio.h>
#include <string.h>
void deleteBook(book_t *lib, int size) {
long searchISBN;
int found = 0;
printf("Enter ISBN to search\n");
if (scanf("%ld", &searchISBN) != 1)
return;
for (int i = 0; i < size;) {
if (lib[i].isbn == searchISBN) {
book_t book = { 0 }; // empty book record
found++;
// display book data before erasing it
printf("Book Name %s\n", lib[i].name);
printf("Book Author %s\n", lib[i].author);
printf("Book ISBN %ld\n", lib[i].isbn);
printf("Book Price %lf\n", lib[i].price);
// copy the remainder elements one position to the left
memmove(lib + i, lib + i + 1, sizeof(*lib) * (size - i - 1))
// reinitialize the last entry
memcpy(lib + size - 1, &book, sizeof(*lib));
// rescan the current entry in case of duplicates
// hence do not increment i
} else {
i++; // test the next entry
}
}
if (found == 0) {
printf("not found");
}
}
You can use a similar technique to insert a new entry at the appropriate position in the table:
void addbook(book_t *lib, int size) {
book_t book = { 0 }; // empty book record
int i, used;
// Loop through the array and pack empty elements
for (i = used = 0; i < size; i++) {
if (lib[i].isbn != 0) {
if (used < i) {
memcpy(lib + used, lib + i, sizeof(*lib));
}
used++;
}
}
// reset unused elements:
for (i = used; i < size; i++) {
if (lib[i].isbn != 0) {
memcpy(lib + i, &book, sizeof(*lib));
}
}
// check if the array is full:
if (used >= size) {
printf("The array is full\n");
return;
}
// Ask for and store the book details to local book structure
printf("Please enter the book name\n");
if (scanf("%s", book.name) != 1)
return;
printf("Please enter the book author\n");
if (scanf("%s", book.author) != 1)
return;
printf("Please enter the book number\n");
if (scanf("%ld", &book.isbn) != 1)
return;
printf("Please enter the book price\n");
if (scanf("%lf", &book.price) != 1)
return;
printf("We will now ask you for the release date of the book by day then month then year");
printf("\nPlease enter release date for this book (dd):");
if (scanf("%d", &book.releaseDate.date) != 1)
return;
printf("\nPlease enter release month for this book (mm):");
if (scanf("%d", &book.releaseDate.month) != 1)
return;
printf("\nPlease enter release year for this book (yyyy):");
if (scanf("%d", &book.releaseDate.year) != 1)
return;
printf("\nDate entered is (%d / %d / %d)",
book.releaseDate.date, book.releaseDate.month, book.releaseDate.year);
//// Loop through the array until you find location to insert book
for (i = 0; i < used; i++) {
if (lib[i].isbn > book.isbn)
break;
}
// book should be inserted at position i
// shift book with larger ISBNs
memmove(lib + i + 1, lib + i, sizeof(*lib) * (used - i));
used++;
// copy book into the array
memcpy(lib + i, &book, sizeof(*lib));
}
For production code, you would need to handle the scanf errors appropriately.
These insertion and deletion methods are not very efficient because on average half the database is copied for every operation. A more efficient implementation would use linked lists to avoid copying the data and make it easier to handle a variable number of books.