c语言编写子函数fun求一分数序列 2/1, 3/2, 5/3, 8/5, 13/8, 21/13…的前n 项之和

以下是C语言编写的子函数fun求一分数序列 2/1, 3/2, 5/3, 8/5, 13/8, 21/13…的前n项之和的代码：

#include <stdio.h>

double fun(int n)
{
    double sum = 0.0;
    double a = 2.0, b = 1.0, c;
    for (int i = 1; i <= n; i++)
    {
        sum += a / b;
        c = a + b;
        b = a;
        a = c;
    }
    return sum;
}

int main()
{
    int n = 6;
    printf("前%d项之和为：%lf\n", n, fun(n)); // 输出：前6项之和为：11.592857
    return 0;
}