Iterator library

Iterators are a generalization of pointers that allow C++ programs to access different containers in a uniform manner. Any algorithm that accepts iterators should accept regular pointers also.

Five iterator categories are defined, according to operations defined on them:

Input iterator	allows reading from the iterator object allows iterating forward without multi-pass guarantee, i. e. reading the same element twice is not guaranteed to produce the same results
Output iterator	allows writing to the iterator object allows iterating forward without multi-pass guarantee
Forward iterator	allows reading from the iterator object allows iterating forward with multi-pass guarantee, i. e. reading the same element twice is guaranteed to produce the same results
Bidirectional iterator	allows reading from the iterator object allows iterating forward and backward with multi-pass guarantee
Random access iterator	allows reading from the iterator object allows iterating forward and backward randomly with multi-pass guarantee

Forward iterators satisfy the requirements of input iterators