foo.cc: In function 'int main()':
foo.cc:8:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
    8 |     for(int i=0;i<a.length();i++){
      |                 ~^~~~~~~~~~~
foo.cc:7:5: warning: unused variable 's' [-Wunused-variable]
    7 | int s=0;
      |     ^

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