foo.cc: In function 'int main()':
foo.cc:9:15: 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<=a.length();i++){
      |              ~^~~~~~~~~~~~
foo.cc:7:7: warning: unused variable 'c' [-Wunused-variable]
    7 |  char c;
      |       ^

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