/in/foo.cc: In function 'int longest(const string&)':
/in/foo.cc:20:48: warning: comparison of integer expressions of different signedness: 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} and 'int' [-Wsign-compare]
   20 |    if (isPalindrome(substr) && substr.length() > max) {
      |                                ~~~~~~~~~~~~~~~~^~~~~
/in/foo.cc:16:6: warning: variable 'start' set but not used [-Wunused-but-set-variable]
   16 |  int start = 0;
      |      ^~~~~