2/1+3/2+5/3+8/5+13/8+...求出该数列前20项的和

#include<stdio.h>int main(){float i=2;float j=1;int n=1;double sum=0.0;for(n=1;n<=20;n++){sum=sum+i/j;i=i+j;j=i-j;}printf("%f\n",sum);return 0;}