#include <valarray>
    TYPE sum() const;

The sum() function returns the summation of all element values using the '+=' operator. If TYPE is not a built-in type, a '+=' operator must exist.

This function does not affect the contents of the valarray.

The following code will return the sum of values in the array:

   #include <valarray>
   #include <iostream>
   const double vd[] = {1,2,3,4,5};
   std::valarray<int> v1(vd,5);
   std::cout << v1.sum() << std::endl;

Will produce this output: