/in/foo.cc: In function 'void left(std::__cxx11::string&)':
/in/foo.cc:12:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=1;i<ss.size();i++) ss[i-1]=ss[i];
              ~^~~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:31:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=1;i<ss.size();i++)
              ~^~~~~~~~~~
/in/foo.cc:38:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<ss.size();i++) s[i].p=i;
              ~^~~~~~~~~~
/in/foo.cc:40:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<ss.size();i++) cout<<s[i].p<<' ';
              ~^~~~~~~~~~