Fibbonacci Number

Your objective for this question is to develop a program which will generate a fibbonacci number. The fibbonacci function is defined as such:

f(0) = 0
f(1) = 1
f(n) = f(n-1) + f(n-2)

Your program should be able to handle values of n in the range 0 to 50.

Input

Each test case consists of one integer n in a single line where 0≤n≤50. The input is terminated by -1.

Output

Print out the answer in a single line for each test case.

Sample Input

3
4
5
-1

Sample Output

2
3
5


        
  

you can use 64bit integer: __int64

思路：最开始想到用递归去解，但是会超时，所以又想到利用数组。            利用数组对每一个算出来的结果都记录下来，这样计算其后的一个可以调用上次计算的结果，所以时间将会被节约。代码：

#include<stdio.h>

void main() {
     long long f[55];
     int n, i;
     while (scanf_s("%d", &n) && n != -1) {
         f[0] = 0;
         f[1] = 1;
         for (i = 2; i <= n; i++) {
             f[i] = f[i - 1] + f[i - 2];
         }
         printf("%I64d\n", f[n]);
     }
}