Use the count_if algorithm with the unary predicate IsEven : Algorithm « vector « C++ Tutorial

1. C++ Tutorial
2. vector
3. Algorithm

#include <algorithm>
#include <vector>
#include <iostream>
using namespace std;
template <typename elementType>
bool IsEven (const elementType& number)
{
    return ((number % 2) == 0);
}

int main ()
{
    vector <int> v;

    for (int nNum = -9; nNum < 10; ++ nNum)
        v.push_back (nNum);

    vector <int>::const_iterator i;
    for ( i = v.begin (); i != v.end (); ++ i )
        cout << *i << ' ';

    cout << v.size () << "' elements" << endl;

    // Use the count_if algorithm with the unary predicate IsEven:
    size_t nNumEvenElements = count_if (v.begin (),v.end (), IsEven <int> );

    cout << "Number of even elements: " << nNumEvenElements << endl;
    cout << "Number of odd elements: ";
    cout << v.size () - nNumEvenElements << endl;

    return 0;
}