说明：  假设你需要指定范围内的随机数，传统的方法是使用ANSI C的函数random(),然后格式化结果以便结果是落在指定的范围内。但是，使用这个方法至少有两个缺点
(suppose you need, within specified limits, random number, the traditional method is to use ANSI C function random (), then formatted results to the results fell within the scope specified. However, the use of this method at least two shortcomings)