C程序设计（第四版）习题5-10

Question

求分数序列
2/1 +3/2+5/3+8/5+13/8+21/13...
前20项之和。

我这样的代码为什么不对啊？输出是21.00000000 答案输出是32.6602607986

 #include <stdio.h> 
int main()
{
    int fenzi(int n);
    int fenmu(int m);
    int i;
    float s=0,tem;
    for(i=1;i<=20;i++)
    {
        tem=fenzi(i)/fenmu(i);
        s=s+tem;
    }
    printf("%f",s);
    return 0;
}
int fenzi(int n)
{
    if(n==1) return 2;
    else if(n==2) return 3;
    else return (fenzi(n-2)+fenzi(n-1));
}
int fenmu(int m)
{
    if(m==1) return 1;
    else if(m==2) return 2;
    else return (fenmu(m-2)+fenmu(m-1));
}

Answer 1

 // ConsoleApplication1.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"

int fenzi(int n);
int fenmu(int m);

int main()
{
    int i;
    float s = 0, tem;
    for (i = 1; i <= 20; i++)
    {
        tem = (double)fenzi(i) / (double)fenmu(i);
        s = s + tem;
    }
    printf("%f", s);
    return 0;
}
int fenzi(int n)
{
    if (n == 1) return 2;
    else if (n == 2) return 3;
    else return (fenzi(n - 2) + fenzi(n - 1));
}
int fenmu(int m)
{
    if (m == 1) return 1;
    else if (m == 2) return 2;
    else return (fenmu(m - 2) + fenmu(m - 1));
}