title: int object is not subscriptable error and list mutability error
body: <p>I am new to using functions, so I'm really stuck here with a few errors.
  When I run the second function, I am getting a 'int object is not subscriptable error' </p>
  
  <p>and When I run the third function, it is changing the list based on the user input as hoped for, but when the program is run again, it shows that the change is not permanent, the list is the same as before the user input change. (its also putting 'None' at the end. </p>