Debugging Challenge #3

Previously on Dr. Lambda's blog:

I have deviced a series of debugging challenges, some are easy, some are really hard, all come from real live systems. Good luck!

The Challenge

• 1 point if you can spot where the error is.
• +1 point if you can explain why.
• +2 points if you can explain how to fix it.

int index = addressLine.Length;
for (int i = 0; i < 10; i++)
{
    int position = addressLine.IndexOf(i.ToString());
    if (position != -1 && position < index)
        index = position;
}
string street = addressLine.Substring(0, index).Trim();
string nr = addressLine
            .Substring(index, addressLine.Length - index)
            .Trim();