程序代码：

# include <stdio.h>

int main(void)
{
    int F1=1, F2=1, Fn, n;
    char c;
    printf("斐波那契数列，请输入n值：
");
    scanf("%d", &n);
    if (n == 1)
        printf("该数是1
");
    else if (n == 2)
        printf("该数是1
");
    else
    {
        for (int i=3; i<=n; ++i)
        {
            Fn=F1+F2;
            F1=F2;
            F2=Fn;
        }
        printf("该数是%d
", Fn);
    }
    printf("是否需要将前四十个数字列出？(Y/N)
");
    scanf("%c", &c);//无论是c=getchar(),还是这个，编译器都直接跳过了这一行，为什么？
    if (c == 'Y')
    {
        int F1=1, F2=1, Fn, n=40, i;
        printf("%5d%5d", 1, 1);
        for (i=3; i<=n; ++i)
        {
            Fn=F1+F2;
            F1=F2;
            F2=Fn;
            printf("%5d", Fn);
            if (n%5 == 0)
                printf("
");
        }
    }
    else
        printf("All right
");

    return 0;
}

程序代码：

#include <stdio.h>

int main(void) {
    unsigned long long F1 = 1, F2 = 1, Fn, n , i = 3;
    char c;
    printf("斐波那契数列，请输入n值：\n");

    while((scanf("%llu", &n)) == 0)
        while(getchar() != '\n');

    while(getchar() != '\n');

    if(n == 1) printf("该数是1\n");

    else if(n == 2) printf("该数是1\n");

    else {
        while(i++ <= n) {
            Fn = F1 + F2;
            F1 = F2;
            F2 = Fn;
        }

        printf("该数是%llu\n", Fn);
    }

    printf("是否需要将前四十个数字列出(Y/N)\n");
    scanf("%c", &c);

    if(c == 'Y' || c == 'y') {
        printf("%10llu %10llu ", F1 = 1, F2 = 1);

        for(i = 3; i <= 40; i++) {
            Fn = F1 + F2;
            F1 = F2;
            F2 = Fn;
            printf("%10llu ", Fn);
            if(i % 5 == 0) printf("\n");
        }

    }
    printf("\nBye!\n");

    return 0;
}