这个文件综合了多种在Ｃ语言中获取当前系统时间的函数。读者可以根据对时间的具体要求，选择其中的函数。-This file is a combination of a variety of access to the function of the current system time in C language. Readers according to the specific requirements of the time, choose the function.

f(n)=f(n-1)+f(n-2) f(0)=f(1)=1，求斐波那契数列第20项，分别用循环和递归的方式，比较时间效率。提示：可以使用c函数clock取出当前系统时间，计算前后各一次，两次相减除以每秒的时钟数，就可以得到以秒为单位的差距-f (n) = f (n-1)+ f (n-2) f (0) = f (1) = 1, Item 20 seeking Fibonacci number Fibonacci sequence that were circulating and recursi