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                       Standard C++ Library
             Copyright 1998, Rogue Wave Software, Inc.


NAME
     count, count_if

      - Count the number of elements in a container that  satisfy
     a given condition.



SYNOPSIS
     #include <algorithm>
     template<class InputIterator, class T>
     typename iterator_traits<InputIterator>::difference_type
     count(InputIterator first, InputIterator last,
           const T& value);
     template <class InputIterator, class T, class Size>
     void count(InputIterator first, InputIterator last,
                const T& value, Size& n);
     template<class InputIterator, class Predicate>
     typename iterator_traits<InputIterator>::difference_type
     count_if(InputIterator first, InputIterator last,
              Predicate pred);
     template <class InputIterator, class Predicate, class Size>
     void count_if(InputIterator first, InputIterator last,
                   Predicate pred, Size& n);



DESCRIPTION
     The count  algorithm  compares  value  to  elements  in  the
     sequence defined by iterators first and last. The first ver-
     sion of count returns the number of matches. The second ver-
     sion  increments  a  counting  value  n each time it finds a
     match. In other words, count returns  (or  adds  to  n)  the
     number  of  iterators i in the range [first, last) for which
     the following condition holds:

     *i == value

     Type T must be EqualityComparable.



COMPLEXITY
     The count_if algorithm lets you  specify  a  predicate,  and
     returns  the  number  of  times  an  element in the sequence
     satisfies the predicate (or  increments  n  that  number  of
     times).  That is, count_if returns (or adds to n) the number
     of iterators i in the range [first, last) for which the fol-
     lowing condition holds:

     pred(*i) == true.

     Both count and count_if perform exactly last-first  applica-
     tions of the corresponding predicate.



EXAMPLE
     //
     // count.cpp
     //
     // Does not demonstrate the partial specialization versions
     // of count and count_if
     //
      #include <vector>
      #include <algorithm>
      #include <iostream>
     using namespace std;

     int main()
      {
       int sequence[10] = {1,2,3,4,5,5,7,8,9,10};
       int i=0,j=0,k=0;
        //
        // Set up a vector
        //
       vector<int> v(sequence,sequence + 10);

       count(v.begin(),v.end(),5,i);  // Count fives
       count(v.begin(),v.end(),6,j);  // Count sixes
        //
        // Count all less than 8
        // I=2, j=0
        //
       count_if(v.begin(),v.end(),bind2nd(less<int>(),8),k);
        // k = 7

       cout << i << " " << j << " " << k << endl;
       return 0;
      }

     Program Output



     2 0 7



WARNINGS
     If your compiler does not  support  partial  specialization,
     then  the  first version of both count and count_if (the one
     that returns the count) is not available.

     If your compiler does not support default  template  parame-
     ters,  then you always need to supply the Allocator template
     argument. For instance, you have to write:

     vector <int, allocator<int> >

     instead of:

     vector <int>

     If your compiler does not support namespaces,  then  you  do
     not need the using declaration for std.

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