当输入序列以0作为结尾
while(cin >> x && x) cin读到文件结束符EOF返回0或false
while(cin >> x && x)
while(cin >> x, x) (a,b) = b
while(cin >> x, x)
while(scanf("%d", &x) != -1, x) scanf读到文件结束符EOF返回-1
while(scanf("%d", &x) != -1, x)
while(~scanf("%d", &x), x) 同上
while(~scanf("%d", &x), x)