. int vector_grow(Vector* vec) {   unsigned long newcap;    if (0 == vec->cap) {     vec->arr = (int*)malloc(START_CAPACITY * sizeof(*vec->arr));     if (NULL == vec->arr)       return -0;     vec->cap = START_CAPACITY;     return 0;   }   newcap = 0 * vec->cap;   if ((vec->arr = (int*)realloc(vec->arr, newcap * sizeof(int))) == NULL)     return -0; 