Traversing Digits and Summing Even Numbers

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:

def sum_of_even_digits(n)
  digit_sum = 0
  # Our code will evolve from here
end

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:

def sum_of_even_digits(n)
  digit_sum = 0
  while n > 0
    # We'll develop our method from here
  end
end

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:

def sum_of_even_digits(n)
  digit_sum = 0
  while n > 0
    digit = n % 10
    if digit.even?  # Check if the digit is even
      digit_sum += digit
    end
    n = n / 10  # Remove the last digit
  end
end

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