In file included from /in/call.cpp:1:
In file included from /in/dlist.h:75:
/in/dlist_impl.h:8:19: error: use of undeclared identifier 'NULL'
        return (first == NULL);
                         ^
/in/dlist_impl.h:17:19: error: use of undeclared identifier 'NULL'
        newfirst->prev = NULL;
                         ^
/in/dlist_impl.h:22:20: error: use of undeclared identifier 'NULL'
                newfirst->next = NULL;
                                 ^
/in/dlist_impl.h:37:13: error: use of undeclared identifier 'NULL'
        np->next = NULL;
                   ^
/in/dlist_impl.h:42:14: error: use of undeclared identifier 'NULL'
                np->prev = NULL;
                           ^
/in/dlist_impl.h:65:15: error: use of undeclared identifier 'NULL'
        if (first == NULL)//which means there is only one element in the list
                     ^
/in/dlist_impl.h:67:10: error: use of undeclared identifier 'NULL'
                last = NULL;
                       ^
/in/dlist_impl.h:71:17: error: use of undeclared identifier 'NULL'
                first->prev = NULL;
                              ^
/in/dlist_impl.h:91:14: error: use of undeclared identifier 'NULL'
        if (last == NULL)//which means there is only one element on list
                    ^
/in/dlist_impl.h:93:11: error: use of undeclared identifier 'NULL'
                first = NULL;
                        ^
/in/dlist_impl.h:97:16: error: use of undeclared identifier 'NULL'
                last->next = NULL;
                             ^
/in/dlist_impl.h:104:9: error: use of undeclared identifier 'NULL'
        :first(NULL), last(NULL)
               ^
/in/dlist_impl.h:104:21: error: use of undeclared identifier 'NULL'
        :first(NULL), last(NULL)
                           ^
/in/dlist_impl.h:109:16: error: use of undeclared identifier 'NULL'
        this->first = NULL;
                      ^
/in/dlist_impl.h:110:15: error: use of undeclared identifier 'NULL'
        this->last = NULL;
                     ^
/in/dlist_impl.h:152:17: error: use of undeclared identifier 'NULL'
        while (here != NULL)
                       ^
16 errors generated.
/in/Compile/Makefile:39: recipe for target 'buildCall' failed
make: *** [buildCall] Error 1