/in/foo.cc: In function 'int main()':
/in/foo.cc:7:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<=s.size();i++){
              ~^~~~~~~~~~
/in/foo.cc:6:6: warning: unused variable 'a' [-Wunused-variable]
  int a,b;
      ^
/in/foo.cc:6:8: warning: unused variable 'b' [-Wunused-variable]
  int a,b;
        ^