foo.cc: In function 'void my_add(std::string, std::string)':
foo.cc:8:30: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
    8 |                 for(int i=0;i<a.length();i++){
      |                             ~^~~~~~~~~~~
foo.cc:17:30: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   17 |                 for(int i=0;i<a.length();i++){
      |                             ~^~~~~~~~~~~
foo.cc:26:22: warning: comparison of integer expressions of different signedness: 'int' and 'long unsigned int' [-Wsign-compare]
   26 |         for(int i=0;i<=sizeof(c);i++){
      |                     ~^~~~~~~~~~~
foo.cc:27:23: warning: iteration 100 invokes undefined behavior [-Waggressive-loop-optimizations]
   27 |                 if(c[i]>'9')c[i]+='A'-'9'-1;
      |                    ~~~^
foo.cc:26:22: note: within this loop
   26 |         for(int i=0;i<=sizeof(c);i++){
      |                     ~^~~~~~~~~~~

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