/in/foo.cc: In function 'int main()':
/in/foo.cc:10:22: 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<s.size();i++)
      |                     ~^~~~~~~~~
/in/foo.cc:20:30: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   20 |         if(t==0)for(int i=0;i<s.size();i++)now+='H';//全部变成最多的字符
      |                             ~^~~~~~~~~
/in/foo.cc:21:30: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   21 |         if(t==1)for(int i=0;i<s.size();i++)now+='T';
      |                             ~^~~~~~~~~
/in/foo.cc:22:30: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   22 |         if(t==2)for(int i=0;i<s.size();i++)now+='U';
      |                             ~^~~~~~~~~
/in/foo.cc:23:30: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   23 |         if(t==3)for(int i=0;i<s.size();i++)now+='1';
      |                             ~^~~~~~~~~
/in/foo.cc:26:22: 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(int i=1;i<s.size();i++)
      |                     ~^~~~~~~~~