用迭代法计算斐波那契数

#include <stdio.h>long fabonacci(int n){long result;long pre_result;long pre_pre_result;result = pre_result = 1;while (n > 2){n -= 1;pre_pre_result = pre_result;pre_result = result;result = pre_result + pre_pre_result;}return result;}int main(){printf("%lu\n", fabonacci(21));}