foo.cc: In member function ‘std::string calculator::add_sub(std::string, std::string, bool)’:
foo.cc:24:40: error: expected unqualified-id before ‘.’ token
   24 |                 for(int i=0;i<max(num1..size(),num2.size());i++)
      |                                        ^
foo.cc:26:29: warning: comparison of integer expressions of different signedness: ‘int’ and ‘std::__cxx11::basic_string<char>::size_type’ {aka ‘long unsigned int’} [-Wsign-compare]
   26 |                         if(i>=num1.size())
      |                            ~^~~~~~~~~~~~~
foo.cc:30:29: warning: comparison of integer expressions of different signedness: ‘int’ and ‘std::__cxx11::basic_string<char>::size_type’ {aka ‘long unsigned int’} [-Wsign-compare]
   30 |                         if(i>=num2.size())
      |                            ~^~~~~~~~~~~~~
foo.cc:46:38: warning: comparison of integer expressions of different signedness: ‘int’ and ‘std::__cxx11::basic_string<char>::size_type’ {aka ‘long unsigned int’} [-Wsign-compare]
   46 |                         for(int i=0;i<num1.size();i++)
      |                                     ~^~~~~~~~~~~~