foo.cc: In function 'void tolower(std::string&)':
foo.cc:6:15: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
    6 |  for(int i=0;i<a.size();i++)
      |              ~^~~~~~~~~
foo.cc: In function 'int strcmp(std::string, std::string)':
foo.cc:11:15: warning: comparison of integer expressions of different signedness: 'int' and 'const long unsigned int' [-Wsign-compare]
   11 |  for(int i=0;i<min(a.size(),b.size());i++){
      |              ~^~~~~~~~~~~~~~~~~~~~~~~

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