c - How to implement a BFS with depth -

i stuck trying think of way to write function bfs depth. wrote working bfs search goes through entire graph thinking of making copy , editing it.

my bfs returns array of int -1 denoting end. thinking after every depth, make marker , put -2 onto array show new depth. example: 0, -2, 1, 4, 6, -2, 3, 5, -1

however, part stuck on. put -2 after first number, -2 after inserting of neighbors of beginning vertex, , on. how write function?

my function looks this:

vertex *bfs(graph *g, vertex v) {    if(v < 0 || v > g->numvertices)       return null;     int size = g->numvertices + 1;    int counter = 0;    int = 0;     queue *fq = createqueue(size);    set *ds = createset(size);     vertex currentv;    vertex *returnarr = (vertex *)malloc(size * sizeof(vertex));    vertex *neighbors;     if(addtoqueue(fq, v) != 1){       printf("error in adding queue\n");       return null;    }     if(addtoset(ds, v) != 1){       printf("error in added set\n");       return null;     }      returnarr[counter] = v;     counter++;      while(queue not empty){       currentv =  top of queue;       neighbors = neighbors(g, currentv);        = 0;       while(neighbors[i] != -1){          if(current element in ds){            addtoset(ds, neighbors[i]);            returnarr[counter] = neighbors[i];            counter++;             addtoqueue(fq, neighbors[i]);          }          i++;       }       free(neighbors);    }     returnarr[counter] = -1;     return returnarr; }