C#

System.Security.Principal.WindowsIdentity.GetCurrent().Name

static int decodeSerial(String serial, byte[] result, int ResLen)
        {

            int m;
            int digit;


            Array.Clear(result, 0, ResLen);

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

                digit = serial[i] - '0';

                
                m = 0;

                do
                {
                    digit += result[m] * 10;
                    result[m++] = (byte)(digit % 255);
                    digit >>= 8;
                }

                while (m < ResLen);

               
                
            }

            return 0;
        }

private static void runAllTests() {
	test("1");
	test("1000");
	test("1000000");
	test("1000000000");
	long j=1;
	for(long i=0; i<63; i++) {
		test(j.ToString());
		j+=j;
	}
	test("-1");
	test("12345678901234567890123456789012345678901234567890123456789012345678901234567890");
}

private static void test(string decimalDigits) {
	try {
		byte[] bytes=decodeSerial(decimalDigits, 10);
		string s=decimalDigits+" = ";
		foreach (byte b in bytes) s+=" "+((int)b).ToString("X2");
		log(s);
	} catch (Exception exc) {
		log(exc.ToString());
	}
}

// returns a little-endian byte array of given size, and representing the multi-precision
// integer value of a positive integer (entered as decimal string) assuming the size suffices.
// example: decodeSerial("1000", 4) returns E8 03 00 00 (4 bytes shown in hex).
private static byte[] decodeSerial(string decimalDigits, int numberOfBytes) {
	byte[] bytes=new byte[numberOfBytes];
	foreach (char c in decimalDigits) {
		int digit="0123456789".IndexOf(c);
		if (digit<0) throw new ArgumentException("bad char in decodeSerial("+decimalDigits+")");
		for (int m=0; m< numberOfBytes; m++) {
			digit+=bytes[m]*10;
			bytes[m]=(byte)(digit&0xFF);
			digit>>=8;
		}
		if (digit!=0) throw new OverflowException("decodeSerial("+decimalDigits+","+numberOfBytes+")");
	}
	return bytes;
}

stephen.darling wrote:

It was hard to explain

stephen.darling wrote:

I have been on with this problem for over 2 months before asking for help

Convert.ToString(n, 16)

stephen.darling wrote:

while (m < ResLen);