template<class InputIterator, class T>
typename iterator_traits<InputIterator>::difference_type
count(InputIterator first, InputIterator last, const T& value);
template<class ExecutionPolicy, class ForwardIterator, class T>
typename iterator_traits<ForwardIterator>::difference_type
count(ExecutionPolicy&& exec, ForwardIterator first, ForwardIterator last, const T& value);
template<class InputIterator, class Predicate>
typename iterator_traits<InputIterator>::difference_type
count_if(InputIterator first, InputIterator last, Predicate pred);
template<class ExecutionPolicy, class ForwardIterator, class Predicate>
typename iterator_traits<ForwardIterator>::difference_type
count_if(ExecutionPolicy&& exec, ForwardIterator first, ForwardIterator last, Predicate pred);
Effects: Returns the number of iterators i in the range [first, last) for which the following corresponding conditions hold: *i == value, pred(*i) != false.