想了很多种赋值的方法,结果怎么都不对,忘大家受累写段算法,谢谢

[CODE]#include <iostream>
using namespace std;
int fib_sum(int f1,int f2,int n){
if (n == 1)
return f1;
if (n == 2)
return f1+f2;

int fn1 = f2,fn2 = f1,fn,sum = fn1+fn2;
for (int i = 3;i <= n;++i){
fn = fn1 + fn2;
sum += fn;

fn2 = fn1;
fn1 = fn;
}
return sum;
}



int main(){
cout << fib_sum(0,1,2) << endl;
system("pause");
return 0;
}[/CODE]

计算前n项和(n > 0)

#include <stdio.h>
int main()
{
int pre=0,curr=1,next,sum=0,n,i;
scanf("%d",&n);
for(i=1;i<=n;i++){
sum+=curr;
next=pre+curr;
pre=curr;
curr=next;
}
printf("%d\n",sum);
}

s_n = f_{n+2} - 1, n>=3. Period.

==============================================================

/*---------------------------------------------------------------------------
File name: FibonacciSum.c
Author: HJin (email: fish_sea_bird [at] yahoo [dot] com )
Created on: 7/25/2007 21:16:00
Environment: Windows XP Professional SP2 English +
Visual Studio 2005 v8.0.50727.762

Modification history:
===========================================================================

Work out the math yourself:

Fibonacci:

f1=f2=1, f_n = f_{n-2} + f_{n-1}, n>=3;

Sum of Fibonacci:

s1=1, s2=2, s_n = s_{n-2} + s_{n-1} + 1 = f_{n+2}-1, n>=3;

1
2
4
7
12
20
33
54
88
143
232
376
609
986
1596
2583
4180
6764
10945
17710
28656
46367
75024
121392
196417
317810
514228
832039
1346268
2178308
3524577
5702886
9227464
14930351
24157816
39088168
63245985
102334154
165580140
267914295
433494436
701408732
1134903169
1836311902
2971215072
4807526975
7778742048
12586269024
20365011073
32951280098
53316291172
86267571271
139583862444
225851433716
365435296161
591286729878
956722026040
1548008755919
2504730781960
4052739537880
6557470319841
10610209857722
17167680177564
27777890035287
44945570212852
72723460248140
117669030460993
190392490709134
308061521170128
498454011879263
806515533049392
1304969544928656
2111485077978049
3416454622906706
5527939700884756
8944394323791463
14472334024676220
23416728348467684
37889062373143905
61305790721611590
99194853094755496
160500643816367087
259695496911122584
420196140727489672
679891637638612257
1100087778366101930
1779979416004714188
2880067194370816119
4660046610375530308
7540113804746346428
Press any key to continue . . .
*/

long long FibonacciSum(int n)
{
long long s=1ll, s1=0ll, s2=1ll;
int i;

for(i=1; i<n; ++i)
{
s=s1+s2+1;
s1=s2;
s2=s;
}

return s;
}

int main()
{
int i;

for(i=1; i<91; ++i)
printf("%lld\n", FibonacciSum(i));

return 0;
}