请问插入 和 删除 出了什么问题

if(is_full(st))
            {
                return false;
            }
            else if (tempi < 1 || tempi > st->id+1)
            {
                return false;
            }
            for (k = st->id; k < tempi-1; k--)
            {
                st->students[k+1] = st->students[k];
            }
            st->students[tempi-1] = val;
            st->id++;
--------------------------------------------------------------------------上面是插入 为什么插入的位子数字被覆盖了



if(is_empty(st))
                    {
                        return false;
                    }
                if (tempi < 1 || tempi > st->id)
                    {
                        return false;
                    }
                for (k = st->id-1; k > tempi-1; k--)
                     {
                        st->students[k-1] = st->students[k];
                     }
                     st->id--;

--------------------------------------------------------------------------为什么一点删除所有的都被删除了