求数列2/1，3/2，5/3，8/5......前二十项之和

#include <iostream>

using namespace std;
int main() {
	int n = 1;
	double sum = 0, i = 1, j = 2, temp = 0;
	while (n <= 20) {
		sum = sum + j / i;
		temp = i; //用中间变量替换，可以很轻松的解决这个问题
		i = j;
		j = i + temp;
		n++;
	}
	cout << "前二十项的和为:" << sum << endl;
	return 0;
}