foo.cc: In function 'int main()':
foo.cc:20:14: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   20 |     while (i < message.length())
      |            ~~^~~~~~~~~~~~~~~~~~
foo.cc:22:63: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   22 |         while (key_map.find(message[i]) != key_map.end() && i < message.length())
      |                                                             ~~^~~~~~~~~~~~~~~~~~
foo.cc:24:63: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   24 |         while (key_map.find(message[i]) == key_map.end() && i < message.length())
      |                                                             ~~^~~~~~~~~~~~~~~~~~

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