/in/foo.cc: In function 'int main()':
/in/foo.cc:29:139: error: invalid conversion from 'char' to 'const char*' [-fpermissive]
   else output((n * 2 + 1) * (n *  2 + 1) + 4 * (n * 2 + 1) + 4 * (n * 2 + 1) * (n - 2) + 4 * ((n - 2) * (n - 3) / 2 + n - 1)), printf('\n');
                                                                                                                                           ^
In file included from /usr/include/c++/6/cstdio:42:0,
                 from /in/foo.cc:1:
/usr/include/stdio.h:364:12: note:   initializing argument 1 of 'int printf(const char*, ...)'
 extern int printf (const char *__restrict __format, ...);
            ^~~~~~