Syntax:
    #include <valarray>
    size_t size() const;
The size() function returns the number of elements in the valarray.
   #include <valarray>
   #include <iostream>
 
   const int vd[] = {1,2,3,4,5};
   std::valarray<int> v1(vd,5);
   std::cout << v1.size() << std::endl;
Will produce this output:
   5