/in/foo.c:66:6: warning: return type of 'main' is not 'int' [-Wmain]
 void main()
      ^~~~
/in/foo.c: In function 'fun':
/in/foo.c:57:17: warning: 'q' may be used uninitialized in this function [-Wmaybe-uninitialized]
         q->next = p->next;
         ~~~~~~~~^~~~~~~~~