Question

So here I am with this simple question

Consider these two for cycles and please
explain to me if there’s any difference
between the two ways of writing

method 1 :

  for(i=(max-1) ; i>=0 ; i--){ do-some-stuff }

method 2 :

  for(i=max ; i>0 ; i--)     { do-some-stuff }

the reason I’m asking this is because today at school
while we were seeing some Java functions, there was
this palindrome method wich would use as max the
length of the word passed to it and the method used
to cycle trough the for was the first, can anyone
clarify me why the person who writed that piece of
code prefeered using that method ?

Answer 1

Yes, there’s a big difference – in the version, the range is [0, max-1]. In the second version, it’s [1, max]. If you’re trying to access a 0-based array with max elements, for example, the second version will blow up and the first won’t.

If the order in which the loop ran didn’t matter, I’d personally use the more idiomatic ascending sequence:

for (int i = 0; i < max; i++)

… but when descending, the first form gives the same range of values as this, just in the opposite order.