Update a struct in Arduino - c

Question

I have one structure like below in Arduino, I want to update it
struct record
{
int bookId;
int qtyInStock;
};
typedef struct record Record;
Record aRec;
aRec.bookId = 100;
aRec.qtyInStock = 12;
aRec.bookId = 101;
aRec.qtyInStock = 10;
aRec.bookId = 102;
aRec.qtyInStock = 100;
If bookId 101 is sold then how can I update qtyInStock? So, qtyInStock for bookId 101 should be 9 now.
Thanks

Answer 1

You can use an array of type record to store multiple books. Sold being your inbuilt function, you can try this:
struct record
{
int bookId;
int qtyInStock;
};
typedef struct record Record;
void sold(int id, Record* records) {
int i;
for(i=0;i<3;i++) {
if(records[i].bookId == id) {
records[i].qtyInStock--;
}
}
}
void updateId(int id, int new_id, Record* records) {
int i;
for(i=0;i<3;i++) {
if(records[i].bookId == id) {
records[i].bookid = new_id;
}
}
}
void updateQty(int id, int new_qty, Record* records) {
int i;
for(i=0;i<3;i++) {
if(records[i].bookId == id) {
records[i].qtyInStock = new_qty;
}
}
}
void main() {
Record records[3];
records[0].bookId = 100;
records[0].qtyInStock = 12;
records[1].bookId = 101;
records[1].qtyInStock = 10;
records[2].bookId = 102;
records[2].qtyInStock = 100;
int i;
sold(101, records);
updateId(100, 99, records);
updateQty(102, 15, records);
for(i=0;i<3;i++) {
printf("%d\n", records[i].bookId);
printf("%d\n\n", records[i].qtyInStock);
}
}

Answer 2

I would keep all records in a linked list, and iterate over them, find the book id, decrease it's available count.
You know that you are editing a single record (aRec) in your example code right? You will need some sort of container for that:
struct node {
Record* value;
Node* next;
}
sruct recordList {
Node* head;
}
/* ... */