C++ std::accumulate doesn't give the expected sum

Question

double numbers[ ] = { 1, 0.5 ,0.333333 ,0.25 ,0.2, 0.166667, 0.142857, 0.125,
                       0.111111, 0.1 } ;
std::vector doublenumbers ( numb         


        

Answer 1

std::accumulate will start to sum the type that is passed as 3rd argument, if you pass an integer, the return type will be int. And in this case implicitly converted to a double.

In C++11 and C++14, if you want to prevent narrowing conversion, you could create an object using direct-list-initialization:

double sum { std::accumulate(doublenumbers.begin(), doublenumbers.end(), 0) };

The compiler will then give you a warning saying that you are trying to convert from int to double and also at which line. This will save you debugging time. And you can easily fix it so that it becomes correct:

double sum { std::accumulate(doublenumbers.begin(), doublenumbers.end(), 0.0) };