Why can't for_each modify its functor argument?

Question

http://www.cplusplus.com/reference/algorithm/for_each/
Unary function taking an element in the range as argument. This can either be a pointer to a

Answer 1

The function object is taken by value. for_each returns the function object, so if you change it to:

multiply = std::for_each(vec.begin(),vec.end(),multiply);

you get the expected output.