C++ Credit Card Validator

Continuing my (almost) daily C++ practice, I am now making a program to check if a credit number is valid or not. The first step was to use the Luhn algorithm, researching this, I learned it was a simple and effective fraud protection algorithm. I broke in down into a few simple steps using this formula and got some test credit card numbers online and attempted the math. It took a little while to get used to, but I got used to it quickly enough. Naturally doing the math is tedious, so I took to Visual Studio 2022 and booted up a C++ file. At first, I created some functions to use later. These were for getting the digits and the sum of the odd and even numbers. Then I created some declarations for each of the functions. I then added some functionality to the main code, mainly prompting the user to input their number and allowing them to do so. Then as a result, adding the sum of the odd and even digits together. For the sum of the even digits, I created a for loop and as I wa...