C#

byte[] data = BitConverter.GetBytes(combined);
if(BitConverter.IsLittleEndian) {
  Array.Reverse(data);
}

Matt Meyer wrote:

you'll need to test for it and reverse the array if needed.

Matt Meyer wrote:

If you're going to be converting the array back into an integer, you'll need to reverse it again since the system is looking for a little-endian byte order.

Matt Meyer wrote:

One minor suggestion - when you're talking hex values, always include the leading zeroes for the data types if the hex number doesn't fit perfectly (eg, 0x075BCD15 instead of 0x75BCD15).

byte[] DecodeRequestCode(string requestCode, int ResLen)
        {
          // Accept a 41 digit string in the format "00000000000000000000000000000000000000"

            int Sum = 0;
            int Digit, Aux, m;
            byte[] result = new byte[17];

            for (int i = 0; i < 41; i++)
            {
                Digit = requestCode[i] - '0';

                Aux = Digit;
                m = 0;

                do
                {
                    Aux += result[m] *10;
                    result[m++] = (byte) (Aux & 255);

                    Aux >>= 8;

                }
                while (m < ResLen);

                

            }

            return result;

        }

string a = "123456789" ;
int b = System.Int32.Parse ( a ) ;
string c = b.ToString ( "x" ) ;
byte[] d = System.Text.Encoding.ASCII.GetBytes ( c ) ;

BigInteger bigInt= 0;
while(remaining.Length > 4){
 bigInt <<= 32;
 byte[] last4 = (last 4 bytes of remaining);
 bigInt += BitConverter.ConvertToUint32(last4);
 remaining = (all but last 4);
}

BobJanova wrote:

Again though I must ask, why not just store your key in hex format in the first place?

BobJanova wrote:

Your key generator could generate keys in the same form but with hex digits.

Application xl = new Application();

var workbooks = xl.Workbooks;
Workbook workbook = workbooks.Open(FileName);

try
{
    Worksheet ws = (Worksheet)workbook.Sheets[1];
    ws.SaveAs(destination, XlFileFormat.xlCSV);
    Marshal.ReleaseComObject(ws);
}
finally
{
    xl.DisplayAlerts = false;
    xl.Quit();
    Marshal.ReleaseComObject(workbook);
    Marshal.ReleaseComObject(workbooks);
    Marshal.ReleaseComObject(xl);
}