creating an address book application that stores entries in a CSV file

Each entry takes a name, address, city, state, zip, and phone.
Display error if any entries other than phone are not entered
Created function to read the file and display all entries. Added delete link with a query string to delete the record.
Created new class named AddressDataStore to handle reading and writing to the CSV file.
Added constructor that sets the $filename property to default to address_book.csv
Allow a user to upload a new CSV file to add entries to the address book.