经典算法详解（1）斐波那契数列的n项

 1 /*斐波那契数列：第一项和第二项为1，后面各项是其前面两项之和*/
 2 /*编写一个函数，输入整数n，求该项的值*/
 3 
 4 #include<iostream>
 5 
 6 using namespace std;
 7 
 8 int fibonacci(int n) {
 9     if (n < 0){
10         return -1;
11     }
12     if ((n == 1 )||( n ==2)) {
13         return 1;
14     }
15     else {
16         int fib_1 = 1,fib_2=1,fib_3;
17         for (int i = 3; i <= n; i++) {
18             fib_3 = fib_1 + fib_2;
19             fib_1 = fib_2;
20             fib_2 = fib_3;
21         }
22         return fib_3;
23     }
24 }
25 
26 int main(int argc, char *argv[]) {
27     cout << "please input n" << endl;
28     int n;
29     cin >> n;
30     cout << "The reslut: " << fibonacci(n) << endl;
31 
32     getchar();
33     getchar();
34     return 0;
35 }