# Credit card numbers follow certain patterns. A credit card number must have between 13 and 16…

patterns. A credit card number must have between 13 and 16 digits.
4 for Visa cards
5 for MasterCard cards
37 for American Express cards
6 for Discover cards
In 1954, Hans Luhn of IBM proposed an algorithm for validating
credit card numbers. The algorithm is useful to determine whether a
card number is entered correctly or is scanned correctly by a
scanner. Almost all credit card numbers are generated following
this validity check, commonly known as the Luhn check or the Mod 10
check. It can be described as follows. (For illustration, consider
the card number 4388576018402626.)
Double every second digit from right to left. If doubling of a
digit results in a two-digit number, add the two digits to get a
single digit number.
2*2 =4, 2*2=4, 4*2=8, 1*2=2, 6*2=12
(1+2 =3), 5*2=10 (1+0=1)
8*2= 16(1+6=7), 4*2=8
Now add all single -digit numbers from step 1.
Add all digits in the odd places from right to left in the card
number.
Sum the results from step 2 and step 3.
If the result from step 4 is divisible by 10, the card number is
valid; otherwise, it is invalid. For example, the number
4388576018402626 is invalid, but the number 4388576018410707 is
valid.
Write a program that prompts the user
to enter a credit card number as a string. Display whether the
number is valid.
Your program should have at least the following functions:
bool isValid (string cardNumber ):
This function returns true if the card number is valid
int sumOfDoubleEvenPlace (string
cardNumber ): This function gets the result from step 2
int getDigit (int number): This
function returns this number if it is a single digit, otherwise,
returns the sum of the two digits
int sumOfOddPlace(string cardNumber ):
This function returns the sum of odd-place digits in the card
number
Do not use any global
variables.

You can use function length() or
size() to ?nd out the number of characters in a string and access
each character in a string by its index. For example:
string word = Hi ;
cout <