/in/foo.cc: In function 'void div(int, int)':
/in/foo.cc:4:6: error: ambiguating new declaration of 'void div(int, int)'
 void div(int x,int y)
      ^~~
In file included from /usr/include/c++/6/cstdlib:75:0,
                 from /usr/include/c++/6/ext/string_conversions.h:41,
                 from /usr/include/c++/6/bits/basic_string.h:5417,
                 from /usr/include/c++/6/string:52,
                 from /usr/include/c++/6/bits/locale_classes.h:40,
                 from /usr/include/c++/6/bits/ios_base.h:41,
                 from /usr/include/c++/6/ios:42,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:1:
/usr/include/stdlib.h:749:14: note: old declaration 'div_t div(int, int)'
 extern div_t div (int __numer, int __denom)
              ^~~