哪里有问题啊？字符数组还是选择法排序？

不知道哪里出错了，数组长度定义小了吗？还是说选择法排序哪里出错了，没有进行排序？求解答，感谢

#include <stdio.h>
struct Book{
double price;
char name[31];
}book;
int main()
{
int n;
char c;
scanf("%d",&n);//读取n之后缓冲区的内容："\n"
struct Book book[n];
int i,max = 0,min = 0;
for(i=0; i<n; i++)
{
gets(book[i].name);
scanf("%lf",&book[i].price);
scanf("%c",&c);//读入缓冲区的"\n"
if(book[i].price>book[max].price)
{
max = i;
}
if(book[i].price<book[min].price)
{
min = i;
}
}
printf("%.2lf, %s\n",book[max].price,book[max].name);
printf("%.2lf, %s\n",book[min].price,book[min].name);
return 0;
}

修改如下，供参考:

#include <stdio.h>
#include <string.h>
struct student {
    char xm[11];
    char bth[9];
    char tel[18];
};
int main()
{
    int n, i, j;
    struct student std[10], tmp;
    scanf("%d", &n);
    for (i = 0; i < n; i++)
        scanf("%s%s%s", std[i].xm, std[i].bth, std[i].tel);
    for (i = 0; i < n - 1; i++) {
        for (j = 0; j < n - 1 - i; j++) {
            if (strcmp(std[j].bth, std[j + 1].bth) > 0)
            {
                tmp = std[j]; std[j] = std[j + 1]; std[j + 1] = tmp;
            }
        }
    }
    for (i = 0; i < n; i++)
        printf("%s %s %s\n", std[i].xm, std[i].bth, std[i].tel);
    return 0;
}