c - Create linked list from elements of a Binary tree at a certain depth -

i trying build linked list, elements @ depth

i came this:

void nivel(abin a, int k, slist *l, int level){     if (!a) return;     if(k == level){      slist n = (slist)malloc(sizeof(struct slist));      n->value = a->value;      n->next=(*l);      (*l) = n;      return;     }else{         nivel(a->left, k, l, level+1);         nivel(a->right, k, l, level+1);     } } 

it work

but exercise asks use header: slist nivel (abin a, int n)

i have tried void practice. can't figure out how make 1 returns linked lists.

data structure , binary tree:

typedef struct slist {     int value;     struct slist* next; } *slist;  typedef struct arvbin* abin; typedef struct arvbin {     int value;     abin right;     abin left; } arvb; 

edit:

<---------------working header in exercise-----------> // thank politank-z

slist nivel_(abin a, int k){     slist *l;       nivel(a, k, l, 1);      return l; }   void nivel(abin a, int k, slist *l, int level){     if (!a) return;     if(k == level){      slist n = (slist)malloc(sizeof(struct slist));      n->value = a->value;      n->next=(*l);      (*l) = n;      return;     }else{         nivel(a->left, k, l, level+1);         nivel(a->right, k, l, level+1);     } } 

regarding difficulty prototype: common restricted function prototype doesn't meet needs of implementation. in such cases, easier call function prototyped function shoehorn functionality prototype.