How to convert string into int array in C#

Question

I am making a credit card validator program in which I am asking for a string which is going to be a 16 digit number (credit card #) and I want to convert that into an int array. How do I do that? I need to then multiply every other digit starting from the first digit by 2.

char[] creditNumbers = creditCardNumber.ToCharArray();

creditNumbers[0] = (char)((int)(creditNumbers[0] * 2));
creditNumbers[2] = (char)((int)(creditNumbers[2] * 2));
creditNumbers[4] = (char)((int)(creditNumbers[4] * 2));
creditNumbers[6] = (char)((int)(creditNumbers[6] * 2));
creditNumbers[8] = (char)((int)(creditNumbers[8] * 2));

This is what I made so far but my casting is not done properly. How do I fix the problem?

First, you should be using a loop, not copying and pasting the same thing over and over. Second, try moving the parenthesis to cast to an int before multiplying, like this: `(char)(((int)creditNumbers[0]) * 2)` — someone, Oct 01 '11 at 21:29
What happens if the digit represents a numerical value `>= 5` and therefore doubling its numerical value doesn't result in a single-digit number? What on earth are you doing to the poor credit cards anyway? — jason, Oct 01 '11 at 21:29
This may help: http://stackoverflow.com/questions/3665757/c-convert-char-to-int — drneel, Oct 01 '11 at 21:31
It's simple. Really simple. First you have to convert the string into an integer variable, and then use the Algorithm for turning a number into digits. The algorithm is one of the first things I have learned in school. Search around the Net to see what I'm talking about. In order to make it universal (to work with N digit numbers) you will have to use loops. — AlexSavAlexandrov, Oct 01 '11 at 21:42
@DBM: Maybe, but converting back to characters is completely misguided. — jason, Oct 01 '11 at 22:01
@svick - because validating *my credit card number* is not left up to programmers that don't know how to parse it? Wishful thinking perhaps, I sure hope not. Kudos to teachers being great at giving out-of-the-box assignments, it always shows. — Hans Passant, Oct 01 '11 at 22:08

svick · Accepted Answer · 2011-10-01T21:50:11.497

8

To just get the int array, I would do this:

creditCardNumber.Select(c => int.Parse(c.ToString())).ToArray()

To check the number using the Luhn algorithm, you could do this:

bool IsValid(string creditCardNumber)
{
    var sum = creditCardNumber.Reverse()
                              .Select(TransformDigit)
                              .Sum();

    return sum % 10 == 0;
}

int TransformDigit(char digitChar, int position)
{
    int digit = int.Parse(digitChar.ToString());
    if (position % 2 == 1)
        digit *= 2;

    return digit % 10 + digit / 10;
}

edited Oct 01 '11 at 21:50

answered Oct 01 '11 at 21:37

svick

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This only shows how to convert String variables to integer variables. – AlexSavAlexandrov Oct 01 '11 at 21:45
1

Which is what the question was actually asking. But I expanded the question to include the complete checksum checking. – svick Oct 01 '11 at 21:52

score 2 · Answer 2 · edited Oct 01 '11 at 21:55

2

var intArray = creditCardNumber.ToCharArray().Select(o => int.Parse(o.ToString())).ToArray();
var result = new List<int>();

for(int i=0; i<intArray.Length; i++){

    if((i % 2) == 0)
      result.Add(intArray[i] * 2);
    else
        result.Add(intArray[i]);
}

Console.Write(string.Concat(result.Select(o => o.ToString())));

edited Oct 01 '11 at 21:55

svick

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answered Oct 01 '11 at 21:43

terjetyl

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How to convert string into int array in C#

2 Answers2