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
