/in/foo.cc: In function 'int main()':
/in/foo.cc:12:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0; i<str.size(); i++){
               ~^~~~~~~~~~~
/in/foo.cc:16:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0; i<str.size(); i++){
               ~^~~~~~~~~~~
/in/foo.cc:10:6: warning: unused variable 'a' [-Wunused-variable]
  int a=0, b=0;
      ^