执行下面C++代码可以找出千位与个位的和恰好等于中间两位的四位数，横线处应该填入（ ）
int count = 0;int a, bc, d, tmp;for (int i = 1000; i <= 9999; i++) { a = (tmp = i) / 1000; _________________________ bc = tmp / 10; d = tmp - bc * 10; if ( a + d == bc) { count++; }}cout << count;