How can I return an error in a loop format if user does not enter inputs in an array format?

I want to ask for error message if user inputs are not entered in a array format. Code is attached below. Please how do I do this?

Answer 1

[Walter Roberson]

use the input option 's' to receive the characters the user entered. Check to be sure that the characters entered match the syntaxes you wish to permit such as requiring that it be of the format

optional whitespace
[
optional whitespace 
one or more decimal digits
optional whitespace 
comma
optional whitespace 
one or more decimal digits 
optional whitespace 
] 
optional whitespace

This check is easy to do using regexp()

Then convert the sequences of digits from characters to numeric

This assumes that you wish to enforce that they use a comma between the parts, refusing (for example) [2 8] for not being in the form you instruct because it does not have the comma.