recursion

代码说明：

说明：  递归，是函数实现的一个很重要的环节，很多程序中都或多或少的使用了递归函数。递归的意思就是函数自己调用自己本身，或者在自己函数调用的下级函数中调用自己。 递归之所以能实现，是因为函数的每个执行过程都在栈中有自己的形参和局部变量的拷贝，这些拷贝和函数的其他执行过程毫不相干。这种机制是当代大多数程序设计语言实现子程序结构的基础，是使得递归成为可能。(Recursion, is a function to achieve a very important part of many programs are more or less use the recursive function. Recursive mean that the function of its own call to themselves or subordinates in their own function calls a function to call their own. Recursion that can be achieved because the function of each execution in the stack has its own shape parameters and local variables of the copy, the copy and the implementation process has nothing to do other functions. This mechanism is the most modern programming language implementation subroutine structure of the foundation is to make recursion possible.)