foo.cc: In function 'int cheng(std::string, std::string)':
foo.cc:7:16: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
    7 |  for(int i=0; i<s1.length(); i++) {
      |               ~^~~~~~~~~~~~
foo.cc:10:16: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   10 |  for(int i=0; i<s2.length(); i++) {
      |               ~^~~~~~~~~~~~
foo.cc:13:16: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   13 |  for(int i=0; i<s1.length(); i++) {
      |               ~^~~~~~~~~~~~
foo.cc:15:17: 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 j=0; j<s2.length(); j++) {
      |                ~^~~~~~~~~~~~
foo.cc:26:1: warning: no return statement in function returning non-void [-Wreturn-type]
   26 | }
      | ^
foo.cc: In function 'int qwe(int, int)':
foo.cc:52:1: warning: control reaches end of non-void function [-Wreturn-type]
   52 | }
      | ^

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