3. Write a C program to create a billing system \& manage the stock register for a small stationary stop. Assume a stationary shop have only the following items: Pen, Pencil, Eraser, Sharpener and geometric box. Assign unique code for each item. Ask the user whether he/she wants to make billing or add items to the stock register. If he/she wants to add items to the stock register, he/she should be asked to enter item name, quantity of each item and cost per piece. Else if he/she wants to make billing, he/she should be asked to enter the item name and quantity of each item. After getting the input during billing, it has to display the total amount including GST. Assume GST of 10% for geometry box and all other items GST is 5%. In addition, it has to update the stock register after billing. It has to display the appropriate error messages like "No sufficient quantity in stock", "Enter a valid item code", etc