foo.cc: In function ‘int main()’:
foo.cc:9:22: warning: comparison of integer expressions of different signedness: ‘int’ and ‘std::__cxx11::basic_string<char>::size_type’ {aka ‘long unsigned int’} [-Wsign-compare]
    9 |         for(int i=1;i<=s.size();i++)
      |                     ~^~~~~~~~~~
foo.cc:12:32: warning: ‘n’ may be used uninitialized [-Wmaybe-uninitialized]
   12 |                         st[++n]=s[i];
foo.cc:8:13: note: ‘n’ was declared here
    8 |         int n;
      |             ^