The following code gives an error when compiled without any options:

$ g++ bug.cc
bug.cc: In function `int main()':
bug.cc:14: error: name lookup of `i' changed for new ISO `for' scoping
bug.cc:8: error:   using obsolete binding at `i'

The preprocessed code:

# 1 "bug.cc"
# 1 "<built-in>"
# 1 "<command line>"
# 1 "bug.cc"
namespace foo
{
  int i;
}

int main()
{
  for (int i=0; i<=10; ++i)
  {
  }

  {
    using namespace foo;
    i = 5;
  }
}

Since at the point of assignment, there is an accessible i (namely foo::i), it
should be used instead of trying to access the for loop variable (which isn't in
scope any more, as the error message correctly points out).

Configured with: ./configure --prefix=/psi/gcc-3.3