Conversion/String Problem

[Stevan]

I was solving Project Eular-Problem 56 ( Problem 56 - Project Euler ), its relatively easy problem.But i encountered a small issue.I was so frustrated cause i couldn't find solution, so i have to google it, eventually i found the problem, and i need an explanation.
The problem was in sum of digits of digit:

   for (int j = 0; j < 10000; j++)
            {
                s = Pdigits[j];
                for (int i = 0; i < s.Length; i++)
                    array[j] += Convert.ToInt32(s[i]);

            }

So here is my code (array Pdigits represent array of numbers), when i sum digits of eg. 99^99 i get 10440, and it should be 936.I just couldn't figure why.I found out that the problem was in

array[j] += Convert.ToInt32(s[i]);

(of course).
Here is the solution.

    for (int j = 0; j < 10000; j++)
            {
                s = Pdigits[j];
                char[] k = s.ToCharArray();
                for (int i = 0; i < s.Length; i++)
                    array[j] += Convert.ToInt32(k[i].ToString());

            }

With using char array k, and then converting it to string i get good output, my question is why?

[Prelude]

Convert.ToInt32(char) doesn't do what you think it does, and s[i] produces a value of char type. It gives you the integer value of the character, not the integer representation of a digit, which is what I assume you're trying to do. Convert.ToInt32(string) does do what you want, which is why converting the character to a string gives you the correct result. You could get the same result with this:

for (int j = 0; j < 10000; j++)
{
    s = Pdigits[j];

    for (int i = 0; i < s.Length; i++)
        array[j] += Convert.ToInt32(s[i].ToString());
}

Or the more classic trick:

for (int j = 0; j < 10000; j++)
{
    s = Pdigits[j];

    for (int i = 0; i < s.Length; i++)
        array[j] += s[i] - '0';
}

[Stevan]

Convert.ToInt32(char) doesn't do what you think it does, and s[i] produces a value of char type. It gives you the integer value of the character, not the integer representation of a digit, which is what I assume you're trying to do. Convert.ToInt32(string) does do what you want, which is why converting the character to a string gives you the correct result. You could get the same result with this:

for (int j = 0; j < 10000; j++)
{
    s = Pdigits[j];

    for (int i = 0; i < s.Length; i++)
        array[j] += Convert.ToInt32(s[i].ToString());
}

Thank you i understand it now.
What i did as a test is printing s[i] (before i made this thread), and i was confused cause i didn't converted it to int, and still i would get numbers printed, which couldn't work if it was a string. Thanks again mate.