/in/P4.cpp: In function 'int main()':
/in/P4.cpp:31:23: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
     for (int i = 0; i < a.size(); ++i) {
                     ~~^~~~~~~~~~
/in/P4.cpp:40:23: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
     for (int i = 0; i < a.size(); ++i) {
                     ~~^~~~~~~~~~
/in/P4.cpp:53:27: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
         for (int i = 0; i < odd.size(); ++i) {
                         ~~^~~~~~~~~~~~
/in/P4.cpp:56:27: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
         for (int i = 0; i < even.size(); ++i) {
                         ~~^~~~~~~~~~~~~
/in/P4.cpp:67:27: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
         for (int i = 0; i < even.size(); ++i) {
                         ~~^~~~~~~~~~~~~
/in/P4.cpp:70:27: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
         for (int i = 0; i < odd.size(); ++i) {
                         ~~^~~~~~~~~~~~
cc1plus: all warnings being treated as errors