Create two parallel arrays as described below:
products[ ] should contain "pen", "paper", "pencil".
inventory[ ] should contain 0.
Create application that will use a function to lookup the product name and return the inventory count for that product. If no product is found it should display "We do not sell this product"
Create a way If you find a match to add or subtract from the product's inventory.
The UI/design is up to you but I should be able to search for pen to return 0. I should be able to add to the inventory count and search again to see the updated inventory.