This is because the statement portion of a do...while loop (the loop's body) is evaluated before the expression portion (the while) is reached, and thus, any declaration in the expression will not be visible during the first iteration of the loop.

Section 11.7: Range-for over a sub-range

Using range-base loops, you can loop over a sub-part of a given container or other range by generating a proxy object that qualifies for range-based for loops.

template<class Iterator, class Sentinel=Iterator> struct range_t {

Iterator b;

Sentinel e;

Iterator begin() const { return b; } Sentinel end() const { return e; }

bool empty() const { return begin()==end(); } range_t without_front( std::size_t count=1 ) const {

if (std::is_same< std::random_access_iterator_tag, typename std::iterator_traits<Iterator>::iterator_category >{} ) {

count = (std::min)(std::size_t(std::distance(b,e)), count);

}

return {std::next(b, count), e};

}

range_t without_back( std::size_t count=1 ) const {

if (std::is_same< std::random_access_iterator_tag, typename std::iterator_traits<Iterator>::iterator_category >{} ) {

count = (std::min)(std::size_t(std::distance(b,e)), count);

}

return {b, std::prev(e, count)};

}

};

template<class Iterator, class Sentinel>

range_t<Iterator, Sentinel> range( Iterator b, Sentinal e ) { return {b,e};

}

template<class Iterable> auto range( Iterable& r ) {

using std::begin; using std::end; return range(begin(r),end(r));

}

template<class C>

auto except_first( C& c ) { auto r = range(c);

if (r.empty()) return r; return r.without_front();

}

now we can do:

std::vector<int> v = {1,2,3,4};

for (auto i : except_first(v)) std::cout << i << '\n';

and print out

2

3

4

Be aware that intermediate objects generated in the for(:range_expression) part of the for loop will have expired by the time the for loop starts.