/*cb35a_c++_STL_算法_for_each

 for_each(b,e,p)

 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()的返回值

 //转换函数operator double()

     //参考：https://www.cnblogs.com/txwtech/p/12115391.html

     //static_cast<double>强制类型转换：

     MeanValue mv=for_each(ivec.begin(), ivec.end(), MeanValue());//for_each的返回值给到mv,mv里面保留了 num与sum的结果。

     cout << "平均值：" << mv.value() << endl;

     double result= for_each(ivec.begin(), ivec.end(), MeanValue());

     //for_each的返回值给到result,result定义为了doubule,它自动调用类型转换函数operator double()

     cout << "平均值2：" << result << endl;

 */

 #include <iostream>

 #include <algorithm>

 #include <vector>

 using namespace std;

 void print(int elem)

 {

     cout << elem << ' ';

 }

 template<class T>

 class AddValue

 {

 private:

     T theValue;

 public:

     AddValue(const T& v) :theValue(v) {}

     void operator()(T& elem) const

     {

         elem += theValue;

     }

 };

 class MeanValue

 {

 private:

     long num;

     long sum;

 public:

     MeanValue() :num(), sum() {}

     void operator()(int elem)//operator就是函数对象

     {

         num++;

         sum += elem;

     }

     double value()

     {

         return static_cast<double>(sum) / static_cast<double>(num);

         //static_cast<double>强制类型转换：

          //https://blog.csdn.net/txwtech/article/details/104148011

     }

     //类型转换函数operator double()，double运算符重载

     //参考：https://www.cnblogs.com/txwtech/p/12115391.html

     operator double()

     {

         return static_cast<double>(sum) / static_cast<double>(num);

     }

 };

 int main()

 {

     vector<int> ivec;

     for (int i = ; i <= ; ++i)

         ivec.push_back(i);

     for_each(ivec.begin(), ivec.end(), print);

     cout << endl;

     for_each(ivec.begin(), ivec.end(), AddValue<int>());//函数对象，自动调用operator

     for_each(ivec.begin(), ivec.end(), print);

     cout << endl;

     for_each(ivec.begin(), ivec.end(), AddValue<int>( *ivec.begin()));

     for_each(ivec.begin(), ivec.end(), print);

     cout << endl;

      // MeanValue()是函数对象，返回也是函数对象

     MeanValue mv=for_each(ivec.begin(), ivec.end(), MeanValue());//for_each的返回值给到mv,mv里面保留了 num与sum的结果。

     cout << "平均值：" << mv.value() << endl;

     double result= for_each(ivec.begin(), ivec.end(), MeanValue());

     //for_each的返回值给到result,result定义为了doubule,它自动调用类型转换函数operator double()

     cout << "平均值2：" << result << endl;

     return ;

 }