程序怎么运行？求解！

分子为前一项分子分母和，分母为1,2,3,5,8，是啥数来着

float fun(int n)
{
    int i;
    int fz = 2;
    int fm = 1;
    int t;
    float sum = 0;
    for(i=0;i<n-1;i++)
    {
        sum += fz*1.0/fm;
        t = fz;
        fz = fm+fz;
        fm = t;
    }
    return sum;
}

/* Note:Your choice is C IDE */
#include "stdio.h"
void main()
{
	/*
	
	数列前20项的和
		2/1,3/2,5/3,8/5,13/8,21/13....
		
		a=1,b=2;
		a1=2,b1=3;
		
		a=a+a1=3;
		b=b+b1=5;
		
		--------------------------
		a1=2,b1=3;
		a =3,b =5;
		---------
		a跟a1交换
		b跟b1交换
		a=2,b=3;
		a1=3,b1=5;
		
		
	*/
    int i;
    double a,a1,b,b1,a2,b2,sum=0;
    //b/a,b1/a1
    a=1,b=2;    //第一项：2/1   a=1,b=2;
    a1=2;b1=3;  //第二项：3/2   a=2,b=3;
      
    	        //第三项：5/3   a1=3,b1=5;
    	        //第四项：8/5   a =5, b=8
    sum = b/a+b1/a1;//前2项的值
    //从第3项开始计算
    for(i=2;i<20;i++)
    {
    	a=a+a1;   //3
    	b=b+b1;   //5
    	sum+= b/a;
    	printf("%0.0lf/%0.0lf+",b,a);
    	a2=a; //a2是临时变量
    	a=a1;
    	a1=a2;

    	b2=b; //b2是临时变量
    	b=b1;
    	b1=b2;
    }
  	printf("=%0.2lf",sum);  
    
}