Modify the program of Example 4.6 so that, in response to the query Do you want to quit (Y/N): the program terminates only if the response is Y or y; continues with a request for another character...

Modify the program of Example 4.6 so that, in response to the query

Do you want to quit (Y/N):

the program terminates only if the response is Y or y; continues with a request for

another character only if the response to the query is N or n; otherwise, repeats the

query.