/in/foo.c: In function 'main':
/in/foo.c:6:5: error: 'cin' undeclared (first use in this function)
    6 |     cin >> x;
      |     ^~~
/in/foo.c:6:5: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:19:5: error: 'cout' undeclared (first use in this function)
   19 |     cout << sum << endl;
      |     ^~~~
/in/foo.c:19:20: error: 'endl' undeclared (first use in this function)
   19 |     cout << sum << endl;
      |                    ^~~~
/in/foo.c:20:16: error: invalid suffix "；" on integer constant
   20 |         return 0；
      |                ^~~
/in/foo.c:20:19: error: expected ';' before '}' token
   20 |         return 0；
      |                   ^
      |                   ;
   21 | }
      | ~