foo.cc: In function 'bool compare(char*, int, std::string)':
foo.cc:9:16: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
    9 |  for(int i=si;i<sub.size()+si;i++)
      |               ~^~~~~~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:22:15: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   22 |  for(int i=0;i<top-sub.size();i++){
      |              ~^~~~~~~~~~~~~~~

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