20.计算速度最快的valarray

 #include <string>
 #include <iostream>
 //用于计算,计算的性能高于vector与array
 #include <valarray>
 #include <algorithm>
 using namespace std;

 void main()
 {
     const double PI = 3.1415926;
     valarray<double> val();
     for (int i = ; i < ; i++)
     {
         val[i] = PI * i*i;
         cout << val[i] << endl;

     }

     valarray<double> valx();
     for (int i = ; i < ; i++)
     {
         valx[i] = cos(i*PI / );
         cout << valx[i] << endl;
     }

     //拥有数组所有的功能
     valarray<char *>my;
     cin.get();
 }