foo.cc: In member function ‘std::string calculator::add_sub(std::string, std::string, bool)’:
foo.cc:18:30: warning: comparison of integer expressions of different signedness: ‘int’ and ‘const long unsigned int’ [-Wsign-compare]
   18 |                 for(int i=0;i<max(num1.size(),num2.size());i++)
      |                             ~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
foo.cc:20:29: warning: comparison of integer expressions of different signedness: ‘int’ and ‘std::__cxx11::basic_string<char>::size_type’ {aka ‘long unsigned int’} [-Wsign-compare]
   20 |                         if(i>=num1.size())
      |                            ~^~~~~~~~~~~~~
foo.cc:24:29: warning: comparison of integer expressions of different signedness: ‘int’ and ‘std::__cxx11::basic_string<char>::size_type’ {aka ‘long unsigned int’} [-Wsign-compare]
   24 |                         if(i>=num2.size())
      |                            ~^~~~~~~~~~~~~
foo.cc:40:38: warning: comparison of integer expressions of different signedness: ‘int’ and ‘std::__cxx11::basic_string<char>::size_type’ {aka ‘long unsigned int’} [-Wsign-compare]
   40 |                         for(int i=0;i<num1.size();i++)
      |                                     ~^~~~~~~~~~~~