题目：取一个整数a从右端开始的4～7位。

程序分析：可以这样考虑：

(1)先使a右移4位。

(2)设置一个低4位全为1,其余全为0的数。可用~(~0<<4)

(3)将上面二者进行&运算。

2.程序源代码：-Topic: take an integer a from the right end of the four to seven began.

Program analysis: it can be to consider:

(1) to make a move to the right four.

(2) sets a low four total for the 1, all the rest for 0 of the number. Can be used to (~ 0 < < 4)

(3) will above the difference and operations.

2. The source code: