foo.cc: In function 'void del(std::string&, int, int)':
foo.cc:12:14: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   12 |         if(si>s1.length())      return;
      |            ~~^~~~~~~~~~~~
foo.cc:13:31: 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(i=si;i<si+len && i<s1.length();i++)
      |                              ~^~~~~~~~~~~~
foo.cc: In function 'void output(std::string)':
foo.cc:21:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   21 |         for (i = 0; i < s1.length(); i++)
      |                     ~~^~~~~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:31:13: warning: unused variable 'i' [-Wunused-variable]
   31 |         int i,si,len;
      |             ^

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