cb35a_c++_STL_算法_for_each

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;

 /*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 ;
 }