Question

Im trying to do a permutation. of five in this case, so 5,4,3,2,1 . Eventually I want it to permute up to 100 which can be stored in my intX class. the calculation is fine, but I want to add up all individual numbers of the output, using the script below.

so 5! = 5x4x3x2x1 = 120 —-> 1+2+0 = 3. BUT My script below gives the output 147:

120
1
2
0
147

What am I doing wrong? I allready tried all converts, I started with just using the string[pointer] thingy, I tried different arrays etc.. but it all keeps coming up with 147. Is it some kind of representation thing?

    static void Main(string[] args)
    {
        IntX total=1;
        IntX totalsum = 0;
        int perm = 5;
        for (int i = perm; i > 0; i--)
        {
            total = total * i;
        }
        Console.WriteLine(total);

        string answerstring = Convert.ToString(total);
        char[] answerArray = answerstring.ToArray();
        for (int x = 0; x < answerArray.Length; x++)
        {
            totalsum += Convert.ToInt32(answerArray[x]);
            Console.WriteLine(answerArray[x]);
        }
        Console.WriteLine(totalsum);
    }

Answer 1

The problem is the way you are converting your answerArray elements back to numbers

Convert.ToInt32(answerArray[x])

The above line takes the char 1 and converts it to an int. This is not the same as parsing it as an int. 1 is ascii character 49 so internally the char has an int representation of 49 and so that is what it is converted to (since this is just trying to do a type conversion rather than any kind of processing)

Similarly 2 = 50 and 0 = 48 so you get the total of 147.

What you want to do is use Integer.Parse to parse strings as numbers. I believe it should implicitly convert the char to a string before parsing it.

So your loop would be:

    for (int x = 0; x < answerArray.Length; x++)
    {
        totalsum += int.Parse(answerArray[x].ToString());
        Console.WriteLine(answerArray[x]);
    }

You can also do it the way others suggested with subtracting chars. This works because the ascii value of 1 is 1 higher than the ascii value for 0. 2 is 2 higher, etc.

Of course this only works with single digit chars. If you ever want to convert more than two digit numbers into int from a string you’ll need int.parse.

For what its worth I suspect that the character subtraction method is the most efficient since it is effectively just doing some very simple type conversion and subtraction. The parse method is likely to do a lot more stuff and so be a bit more heavyweight. I dont’ you will notice a performance difference though.