2/1+3/2+5/3+8/5....前二十项和

#include<stdio.h>int main(){double i=1.0,j=2.0,sum=0.0;int n=0;for(n=1;n<=20;n++){sum=j/i+sum;j=i+j;i=j-i;}printf("%f\n",sum);return 0;}