foo.cc: In function 'int main()':
foo.cc:33:44: warning: comparison of integer expressions of different signedness: 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} and 'int' [-Wsign-compare]
   33 |        (string(ptr->d_name).rfind(".out",l)==l-4||
      |         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~
foo.cc:34:44: warning: comparison of integer expressions of different signedness: 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} and 'int' [-Wsign-compare]
   34 |         string(ptr->d_name).rfind(".ans",l)==l-4))
      |         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~
foo.cc:39:11: warning: ignoring return value of 'char* realpath(const char*, char*)', declared with attribute warn_unused_result [-Wunused-result]
   39 |   realpath(".",s);
      |   ~~~~~~~~^~~~~~~
foo.cc:56:9: warning: ignoring return value of 'int system(const char*)', declared with attribute warn_unused_result [-Wunused-result]
   56 |   system(("cp -f ../../data/"+f+'/'+v[n].second+" "+f+".out").c_str());
      |   ~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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