monline

The correct answer to this question lies in a comment of the most popular answer:

The problem is well known: you enter a number in a cell (or import it or copy&paste it from somewhere else into a spreadsheet) and Excel decides to format ii differently than what you want/expect. Even if you set the cell format to text. Well, there's Excel's "smart" automation at work behind the scenes.

If you want to know everything there's to know about the topic, then I suggest you read all the pages that this site refers to. If you just want an easy to use tool to do the job, check out one of the following MS pages ...

The Excel in MS Office XP (aka. Office 2002) updated with SP3 does not handle leap years correctly. Follow my example to prove it.

Számtalan okot fel lehetne sorolni ... most éppen ez juttatta eszembe.

I was looking for the solution and Google came up with a number of Excel-plugins (third party software) that one can use to do the job. However there's a builtin function that can be used in a number of situations to solve the problem. Here's a nice tutorial on how to do that