第4周项目5-（4）

<span style="font-family:Arial;"></span><pre class="html" name="code">Copyright (c) 2016,
All rights reserced.
<span style="font-family:宋体;FONT-SIZE: 9pt">文件名称：</span><span lang="EN-US" style="font-family:'Arial','sans-serif';FONT-SIZE: 9pt">main.cpp
</span><span style="font-family:宋体;FONT-SIZE: 9pt">作者</span><span style="font-family:'Arial','sans-serif';FONT-SIZE: 9pt"></span><span style="font-family:宋体;FONT-SIZE: 9pt">：李鑫</span><span lang="EN-US" style="font-family:'Arial','sans-serif';FONT-SIZE: 9pt">
</span><span style="font-family:宋体;FONT-SIZE: 9pt">完成日期：</span><span lang="EN-US" style="font-family:'Arial','sans-serif';FONT-SIZE: 9pt">2016.3.24</span>

问题描述：编制递归函数fib(int n)返回第n个Fibnacci数，以此输出Fibnacci序列的第20个数。

#include <iostream>
using namespace std;
int fib(int n);
int main()
{
   cout<<fib(20)<<endl;
   return 0;
}

int fib(int n)
{
    if(n==1)
        return 0;
    else if(n==2)
        return 1;
    else
        return(fib(n-1)+fib(n-2));
}