numbers.cpp: In function 'bool check(const string&)':
numbers.cpp:15:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   15 |     for(int i = 0; i < s.size() / 2; i++){
      |                    ~~^~~~~~~~~~~~~~
numbers.cpp: In function 'bool free(long long int)':
numbers.cpp:24:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   24 |     for(int i = 2; i <=s.size(); i++){
      |                    ~~^~~~~~~~~~
numbers.cpp:25:30: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   25 |         for(int j = 0; j + i <= s.size(); j++){
      |                        ~~~~~~^~~~~~~~~~~