counted ======= ```C++ for(auto x : counted(v)) { ... x.value ... x.index ... } ``` `x.value` is a reference to the element in the container (so you can change it's value), `x.index` is what it is. Container should have forward iterators. This headers is purely a handy tool for the range-based-for-loops (ie `for(auto x : counter(v))`). Using it explicitly with iterators is not recommended! There is no const version of it. Doing `for(const auto x : counted(v))` doesn't make it impossible to change `x` (so the element in the container can be modified). Example: ```C++ for(auto x : counted(v)) { std::cout << "v[" << x.index << "] = " << x.value << std::endl; x.value *= 2; } ``` This will output the container `v`, with it's indeces. And it will multiply every value in `v` by 2.