/in/foo.cc: In function 'int main()':
/in/foo.cc:13:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i = 0; i < s.size() - 2; i++){
                 ~~^~~~~~~~~~~~~~
/in/foo.cc:33:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for(int i = 0; i < s.size() - 1; i++){
                   ~~^~~~~~~~~~~~~~
/in/foo.cc:46:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for(int i = 0; i < s.size() - 1; i++){
                   ~~^~~~~~~~~~~~~~