[FEATURE] Fix the code for better understanding in the list_array.cpp file

[sagarpandyansit]

Detailed Description

Link of the file: https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/data_structures/list_array.cpp

Issues:

1. code for exit does not mention in the list.

Context

• without exit code, the user can not understand how to exit from the infinite while loop.

Possible Implementation

• contributor should write exit code in the console for a better understanding of users.