foo.cc: In function 'int main()':
foo.cc:9:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
    9 |         for(int i=0;i<s.size();i++)
      |                     ~^~~~~~~~~
foo.cc:36:16: warning: suggest parentheses around comparison in operand of '&' [-Wparentheses]
   36 |         if(left==0&right==0){
      |            ~~~~^~~

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