7.2 C控制语句：N以内所有素数判断并输出

示例程序：

#include<stdio.h>
#include<math.h>
int main()
{
    int count = 0, num = 0;
    int MAXN;
    printf("please enter MAXN:\n");
    scanf_s("%d", &MAXN);
    printf("%d以内素数是：\n",MAXN);
    for (int i = 2; i <= MAXN; i++)
    {
        for (int j = 2; j <= sqrt(i); j++)
        {
            if (i%j == 0)
                count++;
        }
        if (count == 0)
        {
                printf("%-5d ", i);
                num++;
                if (num % 10 == 0)
                    printf("\n");
        }
        else
        {
            count = 0;
            continue;
        }
    }
    printf("\n以内素数共计 %d 个 \n", num);
    return 0;
}