foo.cc: In function 'bool ishuiwen(int)':
foo.cc:7:3: error: 'string' was not declared in this scope
   string str = to_string(x);
   ^~~~~~
foo.cc:7:3: note: suggested alternative: 'struct'
   string str = to_string(x);
   ^~~~~~
   struct
foo.cc:8:32: error: 'str' was not declared in this scope
   for (unsigned int i = 0; i < str.size()/2; i++)
                                ^~~
foo.cc: In function 'Listnode* Insert(int*, int)':
foo.cc:27:16: error: 'NULL' was not declared in this scope
     Listnode*t=NULL;
                ^~~~
foo.cc: In function 'int main()':
foo.cc:60:5: error: 'cin' was not declared in this scope
     cin>>n;
     ^~~
foo.cc:60:5: note: suggested alternative: 'main'
     cin>>n;
     ^~~
     main
foo.cc:66:9: error: 'cout' was not declared in this scope
         cout<< h->val <<" ";
         ^~~~

[Hydro](https://hydro.ac)提供评测服务