foo.cc: In function 'int main()':
foo.cc:17:39: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   17 |                 if(i==0&&s2[i]==','||i==s2.size()-1&&s2[i]==',')
      |                                      ~^~~~~~~~~~~~~
foo.cc:17:24: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
   17 |                 if(i==0&&s2[i]==','||i==s2.size()-1&&s2[i]==',')
      |                    ~~~~^~~~~~~~~~~~

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