Creating a C# program that calculates sum of the individual digits of a given number

Question

So for practice, I decided to attempt to create a C# program, that calculates the sum of the individual digits of a given (eg If I were to input the number 123, the sum should be 6, because 1 + 2 + 3..)

My thought process is that I would use a for loop to iterate through a specific number (I'd have to convert the number first to a string though), add each individual number into a list, and then find the sum of that list, in order to get my answer. However, when I do so, as demonstrated by the code below:

static void Main(string[] args)
        {
            int num;
            int sumOfNum = 0;
            List<int> numbersToAdd = new List<int>();

            Console.WriteLine("insert number: ");
            num = Convert.ToInt32(Console.ReadLine());
            string myNum = num.ToString();


            for (int i = 0; i < myNum.Length; i++)
            {
                numbersToAdd.Add(myNum[i]);


            }
            foreach (int n in numbersToAdd)
            {
                sumOfNum = numbersToAdd.Sum();
            }
            Console.WriteLine("the sum is " + sumOfNum);

        } 

Instead of the output is 6, my output instead is 150. I thought it was weird, so when I decided to iterate through my list, so I can see my values, as shown below:

 foreach (int n in numbersToAdd)
            {
                Console.WriteLine(n);
            }

Instead of getting the values 1, 2, and 3, I instead get 49, 50, 51.

Why is that? Is it because of the fact that I'm sending in an index of a string, instead of an actual int? And if so, how can I fix it?

Answer 1

myNum is a string, this means that myNum[i] will return a character and not an int . However, the char is implicitly converted to an int in your case, but you still get the ASCII-value of the character.

In your case, these characters happen to be '1' , '2' and '3' , which have an ASCII-value of 49, 50 and 51 respectively. To see other ASCII values, search the Internet for 'ASCII table'.

To fix your code, you must convert those ASCII-values back to their decimal value by subtracting the value of the '0' -character:

numbersToAdd.Add(myNum[i] - '0');

Apart from that, you don't have to convert the number to a string, you can use modulus 10 to get the right-most digit: num % 10 and then divide num with 10 to advance to the next digit: num /= 10; . Do this in a loop for as long num differs from zero.

while (num > 0)
{
   sumOfNum += num % 10;
   num /= 10;
}