/in/foo.cc: In function 'void rebuild(std::__cxx11::string, std::__cxx11::string, int)':
/in/foo.cc:29:29: warning: converting to non-pointer type 'int' from NULL [-Wconversion-null]
                  tree[n].l =NULL ;
                             ^~~~
/in/foo.cc:36:27: warning: converting to non-pointer type 'int' from NULL [-Wconversion-null]
                 tree[n].r=NULL ;
                           ^~~~
/in/foo.cc: In function 'void jds(int)':
/in/foo.cc:44:17: warning: NULL used in arithmetic [-Wpointer-arith]
  if (tree[n].l==NULL&&tree[n].r==NULL)                              
                 ^~~~
/in/foo.cc:44:34: warning: NULL used in arithmetic [-Wpointer-arith]
  if (tree[n].l==NULL&&tree[n].r==NULL)                              
                                  ^~~~
/in/foo.cc: In function 'void xxu(int)':
/in/foo.cc:58:17: warning: NULL used in arithmetic [-Wpointer-arith]
  if (tree[n].c==NULL)                              
                 ^~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:75:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=1;i<=pre.length();i++)
              ~^~~~~~~~~~~~~~