foo.cc: In function 'int main()':
foo.cc:12:17: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   12 |    for(int j=i;j<a.size();j+=f)
      |                ~^~~~~~~~~
foo.cc:18:17: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   18 |    for(int j=i;j<a.size();)
      |                ~^~~~~~~~~

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