/in/foo.cc: In function 'int main()':
/in/foo.cc:11:14: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
 for(int i=0;i<s1.size();i++)
             ~^~~~~~~~~~
/in/foo.cc:15:14: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
 for(int i=0;i<s2.size();i++)
             ~^~~~~~~~~~