到46项就成了负数  又或者反复试验45项也会发生这样的情况 我试过long定义变量 也会发生这样的问题 求解释啊！！！


#include <stdio.h>

int main (void)
{
     int n;
     int i;
     int f1,f2,f3 ;
   
    f1=1;
    f2=2;
   
    do{
        
        printf("请输入你想知道的菲波拉契序列:");
        scanf("%d",&n);
        
        if(1 == n)
        {
            f3 = f1;
        }
        else if(2 == n)
        {
            f3 = f2;
        }
        else
        {
            for(i=3;i<=n; ++i)
            {
                f3=f1+f2;
                f1=f2;
                f2=f3;
            }
        }
        printf("序列数是：%ld\n",f3);
    }while (1);
        
        
        return 0;
}