I am confused. What is exactly an iterator? and what it is use for?
I know that there is 5 kinds of iterators: input, output, forward, bidirectional and random, but still I am confused.
Anyone could help me to understand.
Thank you.
Iterators are used to traverse containers like list, vector, maps, arrays, etc.

The "kind" of the iterator is decided by what operations it supports. A forward iterator is an iterator that you can go from one element to the next. With a bidirectional iterator you can go both forward and backwards. With a Random access iterator it is possible to go from one element to any other in one step (using an offset). Note that a bidirectional iterator is also a forward iterator, and that a random access iterator is also a bidirectional iterator.

By using function templates it is possible to write functions that works for any kind of iterator of a certain kind. An example is std::sort that works with all types of random access iterators, meaning it can sort arrays, vectors, deques, etc. but not things like std::list because it doesn't have random access iterators.
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A very good introduction to iterators in C++:

The best that I've encountered on the web.
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