Final Project - Shopping Mall

Shopping Mall

# Requirements:
    Users can register, log in and shop
    After the program starts:
    	First print a prompt asking the user to choose an operation to perform
        Since nothing is saved permanently, users must register before they can log in
        Register: ask the user to enter a username and password; the password must be entered twice identically to confirm
             Save the registered user in the program
        Log in: entering the wrong password three times when logging in exits the program
             After a successful login, ask the user to enter their salary, which becomes the user's balance
             The program needs to keep track of the user's login state
        Shopping: 
             Allow the user to buy goods by item number, for example:
             1 iPhone
             2 macbook
             3 bike
             After the user picks an item, check whether the balance is enough; if so, deduct the payment and update the user's balance, otherwise remind the user
             The user can quit at any time; on quitting, print the purchased goods and the balance

Requirements:

1, Write down your own approach to solving the problem, in any form: written description, flowchart, or mind map

2, After finishing the project assignment, take a screenshot & upload the image to check in; submitting the project via GitHub is recommended.

3, Note: after checking in, share it in the study group and @ the teaching assistant to have your code checked