84.计算数列前n项平方根和

已知一个数列从第0项开始的前三项分别是0,0,1，以后的各项都是其相邻的前三项之和，函数fun的功能是：计算并输出该数列前n项的平方根之和，n的值通过形参传入。

#define _CRT_SECURE_NO_WARNINGS#include<stdio.h>#include<math.h>double fun(int n){double sum = 1.0, s0, s1, s2, s3;int k;if (n <= 2)sum = 0;s0 = 0.0;s1 = 0.0;s2 = 1.0;for (k = 4;k <= n;k++){s3 = s0 + s1 + s2;sum += sqrt(s3);s0 = s1;s1 = s2;s2 = s3;}return sum;}int main(){int n;printf("Input N=");scanf("%d", &n);printf("%f\n", fun(n));system("pause");return 0;}