Welcome! In today's lesson, we'll delve into a unique coding challenge that centers around traversing the digits of a number using a while loop under a specific condition. You'll have the opportunity to practice and enhance your skills in working with C#'s loops and conditional statements — fundamental concepts in programming. Are you as excited as I am? Let's dive in!

Today, our objective is to create a method that operates on an integer input. The task might seem simple, but it requires 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 clincher — without converting n into a string. For instance, 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 shot? Great! Let's get started!

To start, we need the basic structure of our method, where we begin by defining a variable digitSum to keep track of the sum of even digits.

Below is the initial platform for our method:

C#
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1public class Solution {
2    public int SumEvenDigits(int n) {
3        int digitSum = 0;
4        // Our code will evolve from here
5        return digitSum;
6    }
7}

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:

C#
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1public class Solution {
2    public int SumEvenDigits(int n) {
3        int digitSum = 0;
4        while (n > 0) {
5            // We'll develop our method from here
6        }
7        return digitSum;
8    }
9}

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 digitSum by this digit.

After processing a digit, we'll then chop off the last digit of n using integer division (n / 10), which allows the while loop to proceed to the next digit. Here's how this appears in the code:

C#
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1public class Solution {
2    public int SumEvenDigits(int n) {
3        int digitSum = 0;
4        while (n > 0) {
5            int digit = n % 10;
6            if (digit % 2 == 0) {  // Check if the digit is even
7                digitSum += digit;
8            }
9            n = n / 10;  // Remove the last digit
10        }
11    }
12}

After summing up all the even digits, the final step is to return our digitSum.

Our complete method now looks like this:

C#
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1public class Solution {
2    public int SumEvenDigits(int n) {
3        int digitSum = 0;
4        while (n > 0) {
5            int digit = n % 10;
6            if (digit % 2 == 0) {  // Check if the digit is even
7                digitSum += digit;
8            }
9            n = n / 10;  // Remove the last digit
10        }
11        return digitSum;
12    }
13}

To run our code and see it in action, we need to include a Main method. This method will create an instance of the Solution class, call SumEvenDigits with a test value, and print the result.

Here is the complete code with the Main method:

C#
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1using System;
2
3public class Solution {
4    public int SumEvenDigits(int n) {
5        int digitSum = 0;
6        while (n > 0) {
7            int digit = n % 10;
8            if (digit % 2 == 0) {  // Check if the digit is even
9                digitSum += digit;
10            }
11            n = n / 10;  // Remove the last digit
12        }
13        return digitSum;
14    }
15
16    public static void Main(string[] args) {
17        Solution solution = new Solution();
18        int result = solution.SumEvenDigits(4625);
19        Console.WriteLine("Sum of even digits: " + result);  // Output should be "Sum of even digits: 12"
20    }
21}

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 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 C# prowess is growing with each challenge you conquer!