/in/foo.cc: In function 'void doing()':
/in/foo.cc:10:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i=0; i<s.size(); i++)
                  ~^~~~~~~~~
/in/foo.cc:26:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i=0; i<s.size(); i++)
                  ~^~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:49:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for(int i=0; i<a.size(); i++)
                      ~^~~~~~~~~