struct in C programming

/* ******************* File name: trans.h ******************* An online store sells 10 items and allow users to add items to their shopping carts then produce an invoice upon completion of each transaction */ struct StockItem{ int s_id; char s_desc[100]; float s_price; } stock_list[10] = { {111, "50\" LED TV", 1500.00}, {112, "75\" Smart LED TV", 12000.00}, {211, "Home Theater", 250.00}, {221, "3D Sound System", 300.00}, {511, "6\" e-reader", 400.00}, {611, "64GB USB Flash Drive", 50.00}, {612, "128GB USB Flash Drive", 95.00}, {621, "64GB Micro SD Card", 75.00}, {711, "7\" Tablet", 300.00},{611, "10.1\" Tablet", 500.00} }; /* A transaction item stores the item's id and quantity */ typedef struct Item{ int item_id; int quantity; } Item; /* A transaction consists of the name of the customer, number of purchased items and array of purchased items */ struct Transaction{ char customer_name[100]; int items_count; Item* items; }; /* 1- read_item reads an item information from the keyboard and returns it */ Item read_item(); /* 2- new_trans prepares a transaction structure with a customer name cn and an empty list of items, the list should big enough to hold (size) Items, and returns a pointer to the transaction */ struct Transaction* new_trans(char* cn, int size); /* 3- purchase_item adds the item (it) to the transaction (tr). If (tr) contains (it) already, just increase the quantity of the corresponding item, otherwise add (it) as a new item */ void purchase_item(struct Transaction* tr, Item it); /* 4- remove_item removes the item (it) from the transaction (tr) if it exists.*/ void remove_item(struct Transaction* tr, Item it); /* 5- calc_total takes a transaction and returns the total amount that should be paid by the customer for this transaction */ float calc_total(struct Transaction* tr); /* 6- main function does the following: - ask the customer to enter his/her name - ask the customer to enter number of items in his transaction - creates a new transaction with a suitable size - reads the items from the keyboard and add them to the transaction - printf an invoice of the transaction in the form: Mr./Mrs. <Customer Name> Total amount: S.R. <Total Amount> */