Fibonacci数列 前n项求和

 public int FibonacciSum(int aVal)
        {
            int sum = 0;
            if (aVal == 0)
            {
                return 0;
            }
            if (aVal == 1)
            {
                return sum = 1;
            }
            else if (aVal == 2)
            {
                return sum = 2;
            }
            else
            {
                int[] Fibo = new int[aVal];
                for (int i = 0; i < aVal; i++)
                {
                    Fibo[0] = 1;
                    Fibo[1] = 1;
                    for (int j = 3; j <= aVal; j++)
                    {
                        Fibo[j - 1] = Fibo[j - 2] + Fibo[j - 3];
                    }
                    sum = sum + Fibo[i];
                }
            }
            return sum;
        }

控制台程序实现

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleUtilities
{
    public class FibonacciSum
    {
        public static void SumFibonacci()
        {
            Console.WriteLine("请输入要求的项数N：");

            //接收控制台传来的数据
            string result = Console.ReadLine();

            int n = Convert.ToInt32(result);

            int[] f = new int[n];   //定义一个整形数组用于存放斐波那契数，好像用整形当项数N大于45时会发生溢出，产生错误结果  
            int sum = 0;            //存放前N项之和  

            //处理特殊情况n<=0
            if (n <= 0)
            {
                Console.WriteLine("项数必须是大与0的整数！");
            }

            //处理特殊情况n=1
            else if (n == 1)
            {
                sum = 1;
                Console.WriteLine("斐波那契数列如下：\n1");
                Console.WriteLine("前" + n + "项之和为： " + sum);
            }

            //处理特殊情况n=2
            else if (n == 2)
            {
                sum = 2;
                Console.WriteLine("斐波那契数列如下：\n1     1");
                Console.WriteLine("前" + n + "项之和为： " + sum);
            }

            //处理一般情况n>=3  
            else
            {
                Console.WriteLine("斐波那契数列如下：");
                for (int i = 0; i < f.Length; i++)
                {
                    f[0] = 1;
                    f[1] = 1;
                    for (int j = 3; j <= n; j++)
                    {
                        f[j - 1] = f[j - 2] + f[j - 3]; //斐波那契数列各项之间的关系，不能用f[j]=f[j-1]+f[j-2],会发生数组越界异常  
                    }
                    Console.WriteLine(f[i] + "\t");
                    sum = sum + f[i];
                    if ((i + 1) % 12 == 0)
                    {   //控制12个数为一行  
                        Console.WriteLine();
                    }
                }
                Console.WriteLine();  //输出一个空行再显示前N项之和  
                Console.WriteLine("前" + n + "项之和为： " + sum);

                Console.Read();
            }
        }
    }
}