Welcome! In today's lesson, we'll explore an intriguing coding challenge that involves traversing the digits of a number using a while loop under specific conditions in Ruby.

This is a great opportunity to practice and enhance your skills in working with Ruby's loops and conditional statements, which are fundamental concepts in programming. Are you ready to dive in? Let's get started!

Today's objective is to create a method that operates on an integer input. The task might seem straightforward, but it demands some ingenuity. Here's the mission: given an integer n, we need to calculate and return the sum of its even digits — and here's the catch — without converting n into a string. For example, if n equals 4625, the output should be 12 because the sum of the even digits 4, 6, and 2 equals 12.

Keep in mind that n will always be a positive integer between 1 and 100_000_000. Ready to give it a try? Excellent! Let's move on!

To start, we need the basic structure of our method, where we define a variable digit_sum to keep track of the sum of even digits.

Below is the initial framework for our method:

This framework establishes a foundation on which we'll incrementally build our solution.

The tool we've chosen to traverse through the digits of the input integer n is the while loop, which is set to run as long as n is greater than zero. Let's incorporate this into our method:

By adding a while loop, we're enabling the method to process each digit of the number one by one.

Inside our loop, we'll first extract the last digit of n using the modulo operation (n % 10). If the digit is even, we'll increase our digit_sum by this digit.

After processing a digit, we'll chop off the last digit of n using integer division (n / 10). Here's how this appears in the method:

This loop processes each digit appropriately, checking for even numbers and updating the sum as needed.

After summing up all the even digits, the final step is to ensure our method returns the digit_sum. In Ruby, the last evaluated expression in a method is implicitly returned, so we simply ensure digit_sum is the last line:

Including digit_sum as the last line ensures that the calculated sum for even digits is returned as the final output of the method.

Well done on completing this lesson! You've successfully navigated the foundational concepts of using a while loop to traverse the digits of a number in Ruby and have gained an understanding of how to apply conditions within it.

Now, it's your turn to apply what you've learned. I invite you to explore additional challenges to solidify and build upon your new skill set. Remember, the only limit to your growth is the boundary of your dedication. Keep practicing; your Ruby prowess is growing with each challenge you conquer!