Lesson-13.md

Lesson 13 Sorry, your car is restricted today 对不起，你的车今天限行

#include <stdio.h>
#include <string.h>

enum 
{ 
	MONDAY=1, 
	TUESDAY, 
	WEDNESDAY, 
	THURSDAY, 
	FRIDAY,
	SATURDAY,
	SUNDAY
};

int is_restricted(int num, int today)
{
	int ret;
	
	switch (num)
	{
		case 0:
		case 5:
			ret = (today == MONDAY) ? 1 : 0;
			break;
			
		case 1:
		case 6:
			ret = (today == TUESDAY) ? 1 : 0;
			break;
			
		case 2:
		case 7:
			ret = (today == WEDNESDAY) ? 1 : 0;
			break;
			
		case 3:
		case 8:
			ret = (today == THURSDAY) ? 1 : 0;
			break;
			
		case 4:
		case 9:
			ret = (today == FRIDAY) ? 1 : 0;
			break;	
			
		default:	
			ret = 0;
			break;	
	}			

	return ret;
}

int main(int argc, char *argv[])
{
	char car_num_str[8] = "N2LG20";
	int tail_num;
	int result;
	
	printf("Please input your car number : \n");
	scanf("%s", car_num_str);
	
	printf("Your car number is <%s> \n", car_num_str);
	tail_num = car_num_str[strlen(car_num_str)-1] - '0';

	printf("the tail number is %d\n", tail_num);
	printf("Today is %s\n", __DATE__);
	
	result = is_restricted(tail_num, MONDAY);
	printf("Total your car is %s \n", result? "restricted" : "permitted");
	
	return 0;
}

知识点

• 枚举 enum
• 分支语句 switch-case
  • break 用法
  • 格式的缩进和对齐
• switch-case 的应用场合
  • 状态机编程
  • printf 函数实现

课堂讨论

• 除了示例中的写法，如果不用 switch-case ，解决这个问题还有其他写法吗？
• 如果考虑到每3个月换一次尾号限行制度，这个程序应该怎么改？

课后练习

• 编写一个程序，统计各个数字，空白字符和其他所有字符出现的次数，以及行数。
• 分析一条格式化打印语句中，打印整数%d，字符%c，字符串%s，地址%p 各自出现的次数。