/in/foo.cc: In function 'int main()':
/in/foo.cc:16:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int j=1;j<str.length();j++){
               ~^~~~~~~~~~~~~
/in/foo.cc:9:8: warning: unused variable 's' [-Wunused-variable]
  int n,s,op;
        ^
/in/foo.cc:9:10: warning: unused variable 'op' [-Wunused-variable]
  int n,s,op;
          ^~