有一分数序列
      2/1，3/2，5/3，8/5，13/8，21/13，……     求前N项之和。
下面两份代码请帮忙改一下。

（1）分子，分母做一序列：
#include<stdio.h>
void main()
{
    int i=1,n,t,x=1,y=2;
    double s,sum=0;
    printf("请输入n=:");
    scanf("%d",&n);
    for(;i<=n;i++)
    {
        s=y/x;
        sum+=s;
        t=y;
        y=y+x;
        x=t;
    }
        printf("前n项之和＝:%f\n",sum);
}

（2）分子，分母各做一序列：

#include<stdio.h>
void main()
{
    int x1=2,x2=3,y1=1,y2=2,n,i=1;
    double s,sum=0;
    printf("请输入n=:");
    scanf("%d",&n);
    for(;i<=n;i++)
    {
        s=x1/y1;
        sum+=s;
        x1=x1+x2;
        x2=x2+x1;
        y1=y1+y2;
        y2=y2+y1;
     }
        printf("前N项之和＝:%ld\n",sum);
}







[ 本帖最后由 zjl01223 于 2011-5-24 14:45 编辑 ]

递归会比较容易理解点！

#include"stdio.h"
double fibonacci(int n);
int main()
{
    double sum,num,deno;
    int n,i=0;
    printf("Input n;\n");
    scanf("%d",&n);
    while(n)
    {
        num=fibonacci(i+1);
        deno=fibonacci(i);
        sum+=num/deno;
        i++,n--;
    }
    printf("%e",sum);
    getch();
    return 0;
}

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

#include<stdio.h>
void main()
{
    double i=1,n,t,x=1,y=2;
    double s,sum=0;
    printf("请输入n=:");
    scanf("%lf",&n);
    for(;i<=n;i++)
    {
        s=y/x;
        sum+=s;
        t=y;
        y=y+x;
        x=t;
    }
        printf("前n项之和＝:%lf\n",sum);
}

数据类型  1/2如果是实数型为0.5 如果是整形为0

楼上很经典啊！！

#include <stdio.h>
#include <time.h>

unsigned int fib_recursive(int);
unsigned int fib_iteration(int);

int main(void) {
    clock_t exec_time = clock();
    printf("%u\n", fib_recursive(37));
    printf("fib_resursive() execution time : %.3f\n", (exec_time = clock() - exec_time) / 1.0 / CLOCKS_PER_SEC);
    printf("%u\n", fib_iteration(37));
    printf("fib_iteration() execution time : %.3f\n", (clock() - exec_time) / 1.0 / CLOCKS_PER_SEC);
    return 0;
}

unsigned int fib_recursive(int n) {
    if(n == 1 || n == 2)
        return 1;
    return fib_recursive(n - 1) + fib_recursive(n - 2);
}

unsigned int fib_iteration(int n) {
    unsigned int start1 = 1, start2 = 1, fib = start2;
    while(n-- > 2) {
        fib = start1 + start2;
        start1 = start2;
        start2 = fib;
    }
    return fib;
}

运行结果：

明显递归效率太低，要是求40递归要用2.5秒左右，而迭代我加到1000都接近0秒。

不得不承认，递归确实效率低！~