Count_if STL Algorithm

Count_if STL Algorithm

The count_if() algorithm returns the number of elements in the sequence beginning at start and ending at end for which the unary predicate and returns true.


template <class InputIterator, class Predicate>
typename iterator_traits<InputIterator>::difference_type
count_if ( ForwardIterator first, ForwardIterator last, Predicate pred );

Return number of elements in range satisfying condition
Returns the number of elements in the range [first,last) for which condition pred is true.

Implementation of count_if() algorithm

#include <iostream>
#include <algorithm>
#include <vector>

using namespace std;

typedef int type;
const int size=10;
const int target=5;

int less_than(int value)
{
 return value<target;
}

int main ()
{
 type const list[size]= {1,3,9,4,20,40};
 vector<type> vec0(list,list+6);
 type result;

result = count_if (vec0.begin(), vec0.end(), less_than);
cout << "contains " << result << " values less that "<< target<< endl;

 return 0;
}// end of main

Program Output:

contains 3 values less that 5
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