foo.cc: In function 'int main()':
foo.cc:13:10: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   13 |  while (i<s.length())
      |         ~^~~~~~~~~~~
foo.cc:16:11: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   16 |   while (j<t.length())
      |          ~^~~~~~~~~~~
foo.cc:10:6: warning: unused variable 'len1' [-Wunused-variable]
   10 |  int len1 = s.length(), len2 = t.length();
      |      ^~~~

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