/in/P4.cpp: In function 'int main()':
/in/P4.cpp:26:23: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
     for (int i = 0; i < numbers.size(); ++i)
                     ~~^~~~~~~~~~~~~~~~
/in/P4.cpp:34:23: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
     for (int i = 0; i < numbers.size(); ++i)
                     ~~^~~~~~~~~~~~~~~~
cc1plus: all warnings being treated as errors