template<class ForwardIterator, class T>
void fill(ForwardIterator first, ForwardIterator last, const T& value);
template<class ExecutionPolicy, class ForwardIterator, class T>
void fill(ExecutionPolicy&& exec,
ForwardIterator first, ForwardIterator last, const T& value);
template<class OutputIterator, class Size, class T>
OutputIterator fill_n(OutputIterator first, Size n, const T& value);
template<class ExecutionPolicy, class OutputIterator, class Size, class T>
OutputIterator fill_n(ExecutionPolicy&& exec,
OutputIterator first, Size n, const T& value);
Requires: The expression value shall be writable ([iterator.requirements.general]) to the output iterator. The type Size shall be convertible to an integral type ([conv.integral], [class.conv]).
Effects: The fill algorithms assign value through all the iterators in the range [first, last). The fill_n algorithms assign value through all the iterators in the range [first, first + n) if n is positive, otherwise they do nothing.
Returns: fill_n returns first + n for non-negative values of n and first for negative values.
Complexity: Exactly last - first, n, or 0 assignments, respectively.