特定的循環操作for_each

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

using namespace std;

template<class Type>
class MultValue
{
private:
	Type factor;
public:
	MultValue(const Type & value):factor(value){}
	void operator() (Type & elem)const { elem = elem * factor;}
};

class Average
{

private:
	long num;
	long sum;
public:
	Average():num(0), sum(0){}
	void operator() (int elem){num++; sum += elem;}
	operator double() 
	{
		return static_cast <double> (sum) / static_cast <double> (num);
	}
};

int main()
{
	vector<int> v1;
	vector<int>::iterator v1_iter;
	int i;
	for (i = -4; i <= 2; i++)
		v1.push_back(i);

	cout << "V1:";
	for (v1_iter = v1.begin(); v1_iter != v1.end(); v1_iter++)
		cout << *v1_iter << " ";
	cout << endl;

	for_each(v1.begin(), v1.end(), MultValue<int> (-2));
	cout << "V1 * -2: ";
	for (v1_iter = v1.begin(); v1_iter != v1.end(); v1_iter++)
		cout << *v1_iter << " ";
	cout << endl;

	for_each(v1.begin(), v1.end(), MultValue<int> (5));
	cout << "v1 * 5: ";
	for (v1_iter = v1.begin(); v1_iter != v1.end(); v1_iter++)
		cout << *v1_iter << " ";
	cout << endl;


	double average = for_each(v1.begin(), v1.end(), Average());
	cout << "average is " << average << endl;


	system("pause");
	exit(0);
}