I agree that this classification of zero is not universal. However, if you make a distinction between the Natural numbers and the Whole numbers, zero is the only element that is different in the two sets. I use the term "counting numbers" to help my students to make the distinction.
"> > Zero is a natural number according to some people such > as Eric Hehner from the University of Toronto. The following > is what he said in one of his books: > > "Your life begins at year 0, a highway begins at mile 0, > and so on."
Of course life begins at year 0, but that is not normally the way people speak. Most people state their age as the number of years completed, not the year of life they are currently in.
I don't understand what you mean by the next paragraph.
> > If we treat the number zero differently, things can get > unnecessarily complicated. For example, if people > used the number zero like the way they use other numbers, > we wouldn't have something like "unchanged" or "<= =>" > in the stock market report.