A palindrome is a string such as “madam”, “radar”, “dad”, and “I”, that reads the same forwards and backwards. The empty string is regarded as a palindrome. Write a recursive function bool isPalindrome(string str, int lower, int upper)
that returns true if and only if the part of the string str in positions lower through upper (inclusive at both ends) is a palindrome. Test your function by writing a main function that repeatedly asks the user to enter strings terminated by the ENTER key. These strings are then tested for palindromicity. The program terminates when the user presses the ENTER key without typing any characters before it.