foo.cc: In function 'int cal(int, int)':
foo.cc:11:19: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   11 |  for(int i = 0; i < s.size(); i ++ )
      |                 ~~^~~~~~~~~~
foo.cc:19:17: warning: comparison of integer expressions of different signedness: 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} and 'int' [-Wsign-compare]
   19 |  while(s.size() < size) s += '0';
      |        ~~~~~~~~~^~~~~~
foo.cc:20:19: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   20 |  for(int i = 0; i < s.size(); i ++ )
      |                 ~~^~~~~~~~~~

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