You're going to have to define your problem better. How do you know when you are visually inspecting the string if 2003 should be added? Once you can lay out a series of steps you would tell your friend to do if he was doing this by hand, then you can tell your friend the computer what to do. :-)

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We are the carpenters and bricklayers of the Information Age.

Don't go borrowing trouble. For programmers, this means Worry only about what you need to implement.

Please remember that I'm crufty and crochety. All opinions are purely mine and all code is untested, unless otherwise specified.