foo.cc: In function 'void del(std::string&, std::string&)':
foo.cc:12:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   12 |         for (j = 0; j < s2.length(); j++)
      |                     ~~^~~~~~~~~~~~~
foo.cc:14:31: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   14 |                 for (i = 0; i < s1.length(); i++)
      |                             ~~^~~~~~~~~~~~~
foo.cc: In function 'void output(std::string)':
foo.cc:26:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   26 |         for (i = 0; i < s1.length(); i++)
      |                     ~~^~~~~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:36:13: warning: unused variable 'i' [-Wunused-variable]
   36 |         int i;
      |             ^

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