STL算法（14）——for_each()

for_each(b,e,p)// 对容器中的数据进行遍历  b和e是一对儿迭代器 p是一个函数或者是函数对象

使用for_each()算法遍历数据

使用for_each()和函数对象修改数据

使用for_each()返回值

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

using namespace std;

void print(int elem)
{
	cout << elem << ' ';
}

// 函数对象
template<class T>
class AddValue
{
private:
	T theValue;
public:
	AddValue(const T &v) : theValue(v){};

	void operator()(T &elem)const
	{
		elem += theValue;
	}
};

class MeanValue
{
public:
	long num;
	long sum;
public:
	MeanValue() :num(0), sum(0){}
	// 定义operator 使其成为函数对象
	void operator()(int elem)
	{
		num++;
		sum += elem;
	}

	double value()
	{
		return static_cast<double>(sum) / static_cast<double>(num);
	}
	operator double()	// 类型转换运算符重载
	{
		return static_cast<double>(sum) / static_cast<double>(num);
	}
};

int main()
{
	vector<int> ivec;
	for (int i = 1; i <= 9; i++)
		ivec.push_back(i);
	cout << endl;

	for_each(ivec.begin(), ivec.end(), print);
	cout << endl;
	MeanValue mv = for_each(ivec.begin(), ivec.end(), MeanValue());
	cout << "平均值：" << mv.value() << endl;
	//for_each(ivec.begin(), ivec.end(), AddValue<int>(10));
	for_each(ivec.begin(), ivec.end(), AddValue<int>(*ivec.begin()));

	for_each(ivec.begin(), ivec.end(), print);
	cout << endl;

	double result = for_each(ivec.begin(), ivec.end(), MeanValue());
	cout << "平均值：" << result << endl;

	//
	system("pause");
	return 0;
}