利用枚举，输入 1~7，输出对应星期几，否则输出 err

#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
enum
{
	MONDAY=1,
	TUESDAY,
	WEDNESDAY,
	THURSDAY,
	FRIDAY,
	SATURDAY,
	SUNDAY
};
int main()
{
	while (1)
	{
		int n = 0;
		printf("请输入1-7的数,0退出\n");
		scanf("%d", &n);
		switch (n)
		{
		case 0:printf("已退出\n");return 0;
		case 1:printf("星期%d\n", MONDAY); break;
		case 2:printf("星期%d\n", TUESDAY); break;
		case 3:printf("星期%d\n", WEDNESDAY); break;
		case 4:printf("星期%d\n", THURSDAY); break;
		case 5:printf("星期%d\n", FRIDAY); break;
		case 6:printf("星期%d\n", SATURDAY); break;
		case 7:printf("星期%d\n", SUNDAY); break;
		default:printf("err\n"); break;
		}
	}
	return 0;
}