std::count, std::count_if

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Defined in header <algorithm>

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template< class InputIterator, class T >

typename iterator_traits<InputIterator>::difference_type

    count( InputIterator first, InputIterator last, const T &value );

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template< class InputIterator, class UnaryPredicate >

typename iterator_traits<InputIterator>::difference_type

    count_if( InputIterator first, InputIterator last, UnaryPredicate p );

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Returns the number of elements in the range [first, last) satisfying specific criteria. The first version counts the elements that are equal to value, the second version counts elements for which predicate p returns Template:cpp.

first, last	-	the range of elements to examine
value	-	the value to search for
p	-	unary predicate which returns ​true for the required elements. The expression p(v) must be convertible to bool for every argument v of type (possibly const) VT, where VT is the value type of InputIterator, regardless of value category, and must not modify v. Thus, a parameter type of VT&is not allowed, nor is VT unless for VT a move is equivalent to a copy(since C++11). ​

Template:returns number of elements satisfying the condition.

linear in the distance between first and last

Template:eq fun cpp Template:example cpp